synthesis between thesis

Synthesis Essays: A Step-by-Step How-To Guide

A synthesis essay is generally a short essay which brings two or more sources (or perspectives) into conversation with each other.

The word “synthesis” confuses every student a little bit. Fortunately, this step-by-step how-to guide will see you through to success!

Here’s a step-by-step how-to guide, with examples, that will help you write yours.

Before drafting your essay:

After reading the sources and before writing your essay, ask yourself these questions:

• What is the debate or issue that concerns all of the writers? In other words, what is the question they are trying to answer?
• On what points do they agree?
• On what points do they disagree?
• If they were having a verbal discussion, how would writer number one respond to the arguments of writer number two?

In a way, writing a synthesis essay is similar to composing a summary. But a synthesis essay requires you to read more than one source and to identify the way the writers’ ideas and points of view are related.

Sometimes several sources will reach the same conclusion even though each source approaches the subject from a different point of view.

Other times, sources will discuss the same aspects of the problem/issue/debate but will reach different conclusions.

And sometimes, sources will simply repeat ideas you have read in other sources; however, this is unlikely in a high school or AP situation.

To better organize your thoughts about what you’ve read, do this:

• Identify each writer’s thesis/claim/main idea
• List the writers supporting ideas (think topic sentences or substantiating ideas)
• List the types of support used by the writers that seem important. For example, if the writer uses a lot of statistics to support a claim, note this. If a writer uses historical facts, note this.

There’s one more thing to do before writing: You need to articulate for yourself the relationships and connections among these ideas.

Sometimes the relationships are easy to find. For example, after reading several articles about censorship in newspapers, you may notice that most of the writers refer to or in some way use the First Amendment to help support their arguments and help persuade readers. In this case, you would want to describe the different ways the writers use the First Amendment in their arguments. To do this, ask yourself, “How does this writer exploit the value of the First Amendment/use the First Amendment to help persuade or manipulate the readers into thinking that she is right?

Sometimes articulating the relationships between ideas is not as easy. If you have trouble articulating clear relationships among the shared ideas you have noted, ask yourself these questions:

• Do the ideas of one writer support the ideas of another? If so, how?
• Do the writers who reach the same conclusion use the same ideas in their writing? If not, is there a different persuasive value to the ideas used by one writer than by the other?
• Do the writers who disagree discuss similar points or did they approach the subject from a completely different angle and therefore use different points and different kinds of evidence to support their arguments?
• Review your list of ideas. Are any of the ideas you have listed actually the same idea, just written in different words?

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In philosophy, the triad of thesis, antithesis, synthesis (German: These, Antithese, Synthese; originally: Thesis, Antithesis, Synthesis) is a progression of three ideas or propositions. The first idea, the thesis, is a formal statement illustrating a point; it is followed by the second idea, the antithesis, that contradicts or negates the first; and lastly, the third idea, the synthesis, resolves the conflict between the thesis and antithesis. It is often used to explain the dialectical method of German philosopher Georg Wilhelm Friedrich Hegel, but Hegel never used the terms himself; instead his triad was concrete, abstract, absolute. The thesis, antithesis, synthesis triad actually originated with Johann Fichte.

1. History of the Idea

Thomas McFarland (2002), in his Prolegomena to Coleridge's Opus Maximum , [ 1 ] identifies Immanuel Kant's Critique of Pure Reason (1781) as the genesis of the thesis/antithesis dyad. Kant concretises his ideas into:

• Thesis: "The world has a beginning in time, and is limited with regard to space."
• Antithesis: "The world has no beginning and no limits in space, but is infinite, in respect to both time and space."

Inasmuch as conjectures like these can be said to be resolvable, Fichte's Grundlage der gesamten Wissenschaftslehre ( Foundations of the Science of Knowledge , 1794) resolved Kant's dyad by synthesis, posing the question thus: [ 1 ]

• No synthesis is possible without a preceding antithesis. As little as antithesis without synthesis, or synthesis without antithesis, is possible; just as little possible are both without thesis.

Fichte employed the triadic idea "thesis–antithesis–synthesis" as a formula for the explanation of change. [ 2 ] Fichte was the first to use the trilogy of words together, [ 3 ] in his Grundriss des Eigentümlichen der Wissenschaftslehre, in Rücksicht auf das theoretische Vermögen (1795, Outline of the Distinctive Character of the Wissenschaftslehre with respect to the Theoretical Faculty ): "Die jetzt aufgezeigte Handlung ist thetisch, antithetisch und synthetisch zugleich." ["The action here described is simultaneously thetic, antithetic, and synthetic." [ 4 ] ]

Still according to McFarland, Schelling then, in his Vom Ich als Prinzip der Philosophie (1795), arranged the terms schematically in pyramidal form.

According to Walter Kaufmann (1966), although the triad is often thought to form part of an analysis of historical and philosophical progress called the Hegelian dialectic, the assumption is erroneous: [ 5 ]

Whoever looks for the stereotype of the allegedly Hegelian dialectic in Hegel's Phenomenology will not find it. What one does find on looking at the table of contents is a very decided preference for triadic arrangements. ... But these many triads are not presented or deduced by Hegel as so many theses, antitheses, and syntheses. It is not by means of any dialectic of that sort that his thought moves up the ladder to absolute knowledge.

Gustav E. Mueller (1958) concurs that Hegel was not a proponent of thesis, antithesis, and synthesis, and clarifies what the concept of dialectic might have meant in Hegel's thought. [ 6 ]

"Dialectic" does not for Hegel mean "thesis, antithesis, and synthesis." Dialectic means that any "ism" – which has a polar opposite, or is a special viewpoint leaving "the rest" to itself – must be criticized by the logic of philosophical thought, whose problem is reality as such, the "World-itself".

According to Mueller, the attribution of this tripartite dialectic to Hegel is the result of "inept reading" and simplistic translations which do not take into account the genesis of Hegel's terms:

Hegel's greatness is as indisputable as his obscurity. The matter is due to his peculiar terminology and style; they are undoubtedly involved and complicated, and seem excessively abstract. These linguistic troubles, in turn, have given rise to legends which are like perverse and magic spectacles – once you wear them, the text simply vanishes. Theodor Haering's monumental and standard work has for the first time cleared up the linguistic problem. By carefully analyzing every sentence from his early writings, which were published only in this century, he has shown how Hegel's terminology evolved – though it was complete when he began to publish. Hegel's contemporaries were immediately baffled, because what was clear to him was not clear to his readers, who were not initiated into the genesis of his terms. An example of how a legend can grow on inept reading is this: Translate "Begriff" by "concept," "Vernunft" by "reason" and "Wissenschaft" by "science" – and they are all good dictionary translations – and you have transformed the great critic of rationalism and irrationalism into a ridiculous champion of an absurd pan-logistic rationalism and scientism. The most vexing and devastating Hegel legend is that everything is thought in "thesis, antithesis, and synthesis." [ 7 ]

Karl Marx (1818–1883) and Friedrich Engels (1820–1895) adopted and extended the triad, especially in Marx's The Poverty of Philosophy (1847). Here, in Chapter 2, Marx is obsessed by the word "thesis"; [ 8 ] it forms an important part of the basis for the Marxist theory of history. [ 9 ]

2. Writing Pedagogy

In modern times, the dialectic of thesis, antithesis, and synthesis has been implemented across the world as a strategy for organizing expositional writing. For example, this technique is taught as a basic organizing principle in French schools: [ 10 ]

The French learn to value and practice eloquence from a young age. Almost from day one, students are taught to produce plans for their compositions, and are graded on them. The structures change with fashions. Youngsters were once taught to express a progression of ideas. Now they follow a dialectic model of thesis-antithesis-synthesis. If you listen carefully to the French arguing about any topic they all follow this model closely: they present an idea, explain possible objections to it, and then sum up their conclusions. ... This analytical mode of reasoning is integrated into the entire school corpus.

Thesis, Antithesis, and Synthesis has also been used as a basic scheme to organize writing in the English language. For example, the website WikiPreMed.com advocates the use of this scheme in writing timed essays for the MCAT standardized test: [ 11 ]

For the purposes of writing MCAT essays, the dialectic describes the progression of ideas in a critical thought process that is the force driving your argument. A good dialectical progression propels your arguments in a way that is satisfying to the reader. The thesis is an intellectual proposition. The antithesis is a critical perspective on the thesis. The synthesis solves the conflict between the thesis and antithesis by reconciling their common truths, and forming a new proposition.

• Samuel Taylor Coleridge: Opus Maximum. Princeton University Press, 2002, p. 89.
• Harry Ritter, Dictionary of Concepts in History. Greenwood Publishing Group (1986), p.114
• Williams, Robert R. (1992). Recognition: Fichte and Hegel on the Other. SUNY Press. p. 46, note 37. 
• Fichte, Johann Gottlieb; Breazeale, Daniel (1993). Fichte: Early Philosophical Writings. Cornell University Press. p. 249. 
• Walter Kaufmann (1966). "§ 37". Hegel: A Reinterpretation. Anchor Books. ISBN 978-0-268-01068-3. OCLC 3168016. https://archive.org/details/hegelreinterpret00kauf. 
• Mueller, Gustav (1958). "The Hegel Legend of "Thesis-Antithesis-Synthesis"". Journal of the History of Ideas 19 (4): 411–414. doi:10.2307/2708045.  https://dx.doi.org/10.2307%2F2708045
• Mueller 1958, p. 411.
• marxists.org: Chapter 2 of "The Poverty of Philosophy", by Karl Marx https://www.marxists.org/archive/marx/works/1847/poverty-philosophy/ch02.htm
• Shrimp, Kaleb (2009). "The Validity of Karl Marx's Theory of Historical Materialism". Major Themes in Economics 11 (1): 35–56. https://scholarworks.uni.edu/mtie/vol11/iss1/5/. Retrieved 13 September 2018. 
• Nadeau, Jean-Benoit; Barlow, Julie (2003). Sixty Million Frenchmen Can't Be Wrong: Why We Love France But Not The French. Sourcebooks, Inc.. p. 62. https://archive.org/details/sixtymillionfren00nade_041. 
• "The MCAT writing assignment.". Wisebridge Learning Systems, LLC. http://www.wikipremed.com/mcat_essay.php. Retrieved 1 November 2015. 

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How to Synthesize Written Information from Multiple Sources

Shona McCombes

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Shona McCombes is the content manager at Scribbr, Netherlands.

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Saul Mcleod, PhD

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Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

On This Page:

When you write a literature review or essay, you have to go beyond just summarizing the articles you’ve read – you need to synthesize the literature to show how it all fits together (and how your own research fits in).

Synthesizing simply means combining. Instead of summarizing the main points of each source in turn, you put together the ideas and findings of multiple sources in order to make an overall point.

At the most basic level, this involves looking for similarities and differences between your sources. Your synthesis should show the reader where the sources overlap and where they diverge.

Unsynthesized Example

Franz (2008) studied undergraduate online students. He looked at 17 females and 18 males and found that none of them liked APA. According to Franz, the evidence suggested that all students are reluctant to learn citations style. Perez (2010) also studies undergraduate students. She looked at 42 females and 50 males and found that males were significantly more inclined to use citation software ( p < .05). Findings suggest that females might graduate sooner. Goldstein (2012) looked at British undergraduates. Among a sample of 50, all females, all confident in their abilities to cite and were eager to write their dissertations.

Synthesized Example

Studies of undergraduate students reveal conflicting conclusions regarding relationships between advanced scholarly study and citation efficacy. Although Franz (2008) found that no participants enjoyed learning citation style, Goldstein (2012) determined in a larger study that all participants watched felt comfortable citing sources, suggesting that variables among participant and control group populations must be examined more closely. Although Perez (2010) expanded on Franz’s original study with a larger, more diverse sample…

Step 1: Organize your sources

After collecting the relevant literature, you’ve got a lot of information to work through, and no clear idea of how it all fits together.

Before you can start writing, you need to organize your notes in a way that allows you to see the relationships between sources.

One way to begin synthesizing the literature is to put your notes into a table. Depending on your topic and the type of literature you’re dealing with, there are a couple of different ways you can organize this.

Summary table

A summary table collates the key points of each source under consistent headings. This is a good approach if your sources tend to have a similar structure – for instance, if they’re all empirical papers.

Each row in the table lists one source, and each column identifies a specific part of the source. You can decide which headings to include based on what’s most relevant to the literature you’re dealing with.

For example, you might include columns for things like aims, methods, variables, population, sample size, and conclusion.

For each study, you briefly summarize each of these aspects. You can also include columns for your own evaluation and analysis.

The summary table gives you a quick overview of the key points of each source. This allows you to group sources by relevant similarities, as well as noticing important differences or contradictions in their findings.

Synthesis matrix

A synthesis matrix is useful when your sources are more varied in their purpose and structure – for example, when you’re dealing with books and essays making various different arguments about a topic.

Each column in the table lists one source. Each row is labeled with a specific concept, topic or theme that recurs across all or most of the sources.

Then, for each source, you summarize the main points or arguments related to the theme.

The purposes of the table is to identify the common points that connect the sources, as well as identifying points where they diverge or disagree.

Step 2: Outline your structure

Now you should have a clear overview of the main connections and differences between the sources you’ve read. Next, you need to decide how you’ll group them together and the order in which you’ll discuss them.

For shorter papers, your outline can just identify the focus of each paragraph; for longer papers, you might want to divide it into sections with headings.

There are a few different approaches you can take to help you structure your synthesis.

If your sources cover a broad time period, and you found patterns in how researchers approached the topic over time, you can organize your discussion chronologically .

That doesn’t mean you just summarize each paper in chronological order; instead, you should group articles into time periods and identify what they have in common, as well as signalling important turning points or developments in the literature.

If the literature covers various different topics, you can organize it thematically .

That means that each paragraph or section focuses on a specific theme and explains how that theme is approached in the literature.

Source Used with Permission: The Chicago School

If you’re drawing on literature from various different fields or they use a wide variety of research methods, you can organize your sources methodologically .

That means grouping together studies based on the type of research they did and discussing the findings that emerged from each method.

If your topic involves a debate between different schools of thought, you can organize it theoretically .

That means comparing the different theories that have been developed and grouping together papers based on the position or perspective they take on the topic, as well as evaluating which arguments are most convincing.

Step 3: Write paragraphs with topic sentences

What sets a synthesis apart from a summary is that it combines various sources. The easiest way to think about this is that each paragraph should discuss a few different sources, and you should be able to condense the overall point of the paragraph into one sentence.

This is called a topic sentence , and it usually appears at the start of the paragraph. The topic sentence signals what the whole paragraph is about; every sentence in the paragraph should be clearly related to it.

A topic sentence can be a simple summary of the paragraph’s content:

“Early research on [x] focused heavily on [y].”

For an effective synthesis, you can use topic sentences to link back to the previous paragraph, highlighting a point of debate or critique:

“Several scholars have pointed out the flaws in this approach.” “While recent research has attempted to address the problem, many of these studies have methodological flaws that limit their validity.”

By using topic sentences, you can ensure that your paragraphs are coherent and clearly show the connections between the articles you are discussing.

As you write your paragraphs, avoid quoting directly from sources: use your own words to explain the commonalities and differences that you found in the literature.

Don’t try to cover every single point from every single source – the key to synthesizing is to extract the most important and relevant information and combine it to give your reader an overall picture of the state of knowledge on your topic.

Step 4: Revise, edit and proofread

Like any other piece of academic writing, synthesizing literature doesn’t happen all in one go – it involves redrafting, revising, editing and proofreading your work.

Checklist for Synthesis

•   Do I introduce the paragraph with a clear, focused topic sentence?
•   Do I discuss more than one source in the paragraph?
•   Do I mention only the most relevant findings, rather than describing every part of the studies?
•   Do I discuss the similarities or differences between the sources, rather than summarizing each source in turn?
•   Do I put the findings or arguments of the sources in my own words?
•   Is the paragraph organized around a single idea?
•   Is the paragraph directly relevant to my research question or topic?
•   Is there a logical transition from this paragraph to the next one?

Further Information

How to Synthesise: a Step-by-Step Approach

Help…I”ve Been Asked to Synthesize!

Learn how to Synthesise (combine information from sources)

How to write a Psychology Essay

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How to write a synthesis essay

• January 1, 2024

Synthesis essay is a challenging form of academic writing in which you combine multiple sources into a coherent and persuasive argument.

When writing one, better follow a series of basic steps that we will explain in the next paragraphs to write a great essay.

So let’s quickly start learning how to write a great synthesis essay.

Quick summary

• Take the time to understand the essay prompt to grasp the requirements of the assignment.
• Engage in extensive research and gather information from a variety of reputable sources.
• Develop a strong thesis statement and outline.
• Start writing your introduction, body paragraphs, and conclusion. Make sure to include smooth transitions between these paragraphs.
• Use the proper citation or formatting (APA, MLA, etc.) and make sure you proofread your essay.

Synthesis essay definition

What is a synthesis essay?

Your primary goal with a synthesis essay is to provide a unique perspective, supported by evidence. For example, suppose you have two distinct essays or research papers on “excessive social media usage” and “the effects of social media on psychology.”

In your synthesis essay, you can blend these two sources into a cohesive argument like “the psychological impacts of excessive social media usage on individuals.”

Synthesis essay introduction

The introduction is the opening paragraph of a synthesis essay, where you present the topic and provide background information. Like a usual introduction , it should not be more than 10% of your essay.

• It should include a clear and concise thesis statement that states the main argument or viewpoint of the essay.
• It should reflect the synthesis of information from multiple sources.

Now let’s have a look at the introduction example below. 

Synthesis essay introduction example

Introduction, body paragraphs.

The body paragraphs form the core of the synthesis essay. Each paragraph should focus on a specific aspect of the argument and present evidence and analysis from the sources to support the thesis statement. When writing body paragraphs: 

• Use topic sentences to introduce the main idea of each paragraph
• Make use of transition words to create a smooth flow between paragraphs.

Let’s have a look at a body paragraph example.

Synthesis essay body paragraph example

Synthesis essay conclusion.

The conclusion is the final paragraph of your essay. A compelling conclusion leaves a lasting impact on the reader, reinforcing the essay’s main message. 

• Restate the thesis statement slightly different.
• Summarize the main points discussed in the body paragraphs and emphasize the significance of the overall synthesis 

Let’s have a look at the components of a conclusion paragraph below. 

Synthesis essay conclusion example

Now that we’ve seen a short example of synthesis essay, let’s continue with the steps to write a great one.

Steps on writing a synthesis essay

In this section, we’ll guide you through the writing process with each steps explained in detail and examples. 

Step 1 - Understand your assignment

• Depending on your field of study, you may need to adhere to standard formatting styles such as MLA , APA , or Chicago.
• Consider that formatting expectations may be different. Pay attention to certain guidelines provided by your instructor.

Example of a synthesis essay assignment

• Investigate the impact of artificial intelligence on the job market and society.
• Synthesize at least three different sources, including academic articles, news reports, and opinion pieces, to discuss the benefits and challenges posed by AI's integration into various industries.
• Consider the ethical implications, potential job displacement, and the role of policymakers in addressing these changes.
• Use correct APA 7 citation format and make sure the essay is at least 1000 words.

So you see an example above, take some time to carefully review the prompt, and give particular attention to the formatting requirements. 

Step 2 - Read and annotate the sources

After finding relevant sources, read each one critically by highlighting key ideas and arguments. Annotating sources with concise summaries and evaluative comments helps in later stages of the essay writing process.

• Academic Journals and Research Papers: These are scholarly articles written by experts in a particular field.
• Books: Books: written by reputable authors and published by well-known publishers can be valuable sources of information.
• Government Publications: Reports, statistics, and studies published by government agencies can be reliable sources of data.
• Newspapers and Magazines: Articles from reputable newspapers and magazines can offer current and relevant information on various topics.

Step 3 - Draft a thesis statement

A well-crafted thesis statement forms the basis of any synthesis paper. It serves as the central argument, summarizing the synthesis of information gathered from selected sources. 

A compelling thesis statement should be clear, concise, and debatable as it sets the tone for the entire paper. 

Synthesis essay thesis statement example

....(introduction starts) ....(introduction continues) ....(introduction continues) The pursuit of space exploration has had profound effects on scientific advancement, global cooperation, and technological innovation, and has also raised ethical considerations. Thesis statement, which is usually the last sentence of your introduction

Step 4 - Create an outline

Creating an outline helps to organize the structure of the essay systematically. Using a formal approach with Roman numerals allows for an orderly arrangement of topics and supporting details.

With an outline , you can use subcategories to cite specific points and integrate references to various sources. Or simply structure your whole essay before you start. 

Synthesis essay outline example

Outline sample

• Hook sentence
• Background information
• Thesis statement (Your argument & claim)
• Topic sentene
• Supporting detail 1
• Supporting detail 2
• Supporting evidence
• Topic sentence
• Counterpoint
• Restatement of thesis
• Summarize main points
• Closing sentence

Step 5 - Start writing your essay

With the outline, structure your essay into introduction , body paragraphs , and conclusion .  

First draft won’t be perfect, no worries. Here you simply start writing your essay from intro to the conclusion. 

Refer to our Introduction-Body-Conclusion examples above to complete this step!

Step 6 - Proofread your essay

• Make sure your grammar is accurate and clear. If possible, use tools like Grammarly .
• Read aloud your essay to notice details and mistakes.
• Let your essay sit for a couple days and make someone else read it. They may notice the mistakes you've overseen.
• Utilize an AI paraphrasing tool to check for any potential improvements in sentence structure and wording.

5-Paragraph Synthesis Essay Example

So now that you’ve seen all steps of writing a synthesis essay, it’s time to analyze a 5-paragraph example to have practical information. Simply see the essay example below and analyze how each sentence contributes to overall structure of essay. 

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And that’s all for today. If you want to keep learning more about academic writing, feel free to visit our extensive Learning Center or YouTube Channel . 

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Synthesis Essay Examples

A synthesis essay is another piece of academic discourse that students often find difficult to write. This assignment indeed requires a more nuanced approach to writing and performing research. It’s particularly relevant to students taking an AP English Language and Composition exam, so learning how to write a synthesis essay is crucial to getting a high score.

This article will explore the definition of a synthesis essay, its functions, and objectives, and provide a tutorial on how to write a synthesis essay.

What is a synthesis essay?

To understand how to write a synthesis essay, we first need to figure out why it is called this way.

The word “synthesis” comes from the Greek language where it means “composition” or “collection.” This means that a synthesis essay can be interpreted as a piece of writing that combines something together. But what?

The Advanced Placement (AP) Program known for developing complex courses for high-school students includes a synthesis essay as one of its Language and Composition exam questions. In it, the AP Program asks students to analyze several sources of information and write an essay that “synthesizes” (or incorporates) evidence from some of the sources.

Thus, a synthesis essay is a written text that explores a certain issue using perspectives derived from multiple different sources.

Synthesis essay: format and objectives

Unlike other types of academic analysis, synthesis questions do not aim to evaluate the overall persuasiveness of your arguments. As a writer, you should aim to analyze, evaluate, and integrate diverse ideas into a coherent whole. Here are some of the skills students need to demonstrate in their synthesis essays:

• Analyzing sources . Before you learn how to start a synthesis essay, your task is to read and analyze the sources presented to you and understand what they’re about.
• Assessing the arguments . After familiarizing yourself with the available sources, you are supposed to evaluate if the arguments they support are strong or weak, which will help you determine the course of your essay.
• Identifying common positions . The next skill you must demonstrate is identifying common positions across the sources. By comparing and contrasting different viewpoints, the writer should be able to detect repeating ideas that contribute to a deeper understanding of the topic.
• Integrating sources . Your main task in a synthesis essay is combining ideas from different authors to create a cohesive argument. This will help you show how well you can extract information from various sources.

As you see, the chief goal of synthesis questions is to show how well you can analyze sources and derive information from them.

How to start a synthesis essay: tutorial

During an AP examination, you don’t have a lot of time to write the text. It can be stressful, and it’s not rare for students to panic and forget what to do. Don’t worry, with these simple steps, you’ll be able to create a great synthesis essay and ace your exam.

1. Scan the given sources

At first, you will be handed six sources that you’re supposed to briefly examine. These can include academic and newspaper articles, graphs, schedules, prompts, and other documents that can be used to support your future thesis statement.

Remember that you don’t have a lot of time, so take a quick look at the documents and leave short remarks that can help you remember which source supports or argues a certain opinion.

2. Develop your stance

After you’ve studied the sources, it’s time to come up with your stance and thesis statement. Note that, unlike other essays, the stance you must take in your synthesis essay might not correlate with your actual opinion.

Your task is to choose a position that you can support with the sources provided to you. This will showcase your ability to draw an unbiased and logical conclusion from a wide range of references. However, your stance should express an original idea and cannot paraphrase the points given in the source texts.

3. Write your essay

Your essay should start with a two or three-sentence-long introduction that gives background to the topic you’re going to be writing about. It should also include your thesis – the idea based on the evidence you’ve gathered that you’re going to defend in the next part of your essay. Don’t use personal pronouns as a synthesis essay provides an overview of facts instead of your opinion

The body of your synthesis essay should be built of several arguments. Each argument should refer to a specific part of your thesis and provide evidence to support the claims. Use the sources provided to you as evidence to validate your arguments. You should use at least three sources, but the more you incorporate in your text, the better. You can draw arguments and evidence from your background knowledge or include counter-arguments from the remaining sources. When you refer to the original documents, make sure to include the number of the source in brackets at the end of a sentence.

In your conclusion, restate your original thesis and summarize what you stated before. Don’t repeat the same thoughts. Instead, include a new idea you haven’t mentioned before or a call to action to finish your essay properly.

Synthesis essay: examples

The list of sources provided as part of the examination:

• A New York Times article about the relevance of blue-collar workers;
• A Washington Post article about the uselessness of art degrees;
• The Economist’s article about the decreasing wages of college graduates;
• A New Your Times article proving that college does pay off;
• An article about a businessman giving money to teens to start businesses instead of going to college
• A survey on whether college education is worth it

Is college worth it?

In the current era of shifting economic landscapes and evolving societal expectations, the value of higher education has become a subject of intense scrutiny. While some decades ago, a college education was considered the only solution to a better life, nowadays this sentiment is no longer relevant. Higher education can no longer guarantee high salaries and employment, not to mention the unbearable strain it puts on a future graduate’s finances.

The modern world of employment has shifted. While decades ago society needed information-centric professionals, now the situation is different. With the Internet, employers can now find new hires from all over the world with much cheaper salary expectations, leaving local college graduates with no choice but to agree to a lower pay than they expected[3]. This demonstrates the new trend of decreasing rewards for higher education that is very likely to continue in the future.

Another issue is the lack of employment in certain areas. It is no secret that Art and Humanities graduates have a tough time finding positions with adequate pay in the field they studied[2]. Many of them have to search for employment in other fields that have nothing to do with their degrees, which further proves that higher education does not provide job security.

Furthermore, the cost of higher education in America has been the subject of many debates. Even with scholarships and financial aid, many students still find themselves facing daunting loan repayments upon graduation[6]. This financial pressure can delay important milestones such as buying a home, starting a family, or saving for retirement. Additionally, the job market may not always align with graduates' expectations, making it challenging to secure well-paying positions to effectively manage their debt. As a result, the financial impact of college can be felt long after receiving a diploma, shaping the economic landscape of young professionals for years to come.

In conclusion, higher education no longer offers guaranteed employment and financial stability benefits, often leaving graduates with an exorbitant debt they can not afford. Because of this, the governments should reevaluate their current educational and economic policies and develop other areas of education like vocational schools to provide stability to future generations.

Conclusion: Writing a synthesis essay

A synthesis essay tests your ability to conduct objective analysis and derive facts from multiple different references. It helps you learn to put aside your personal bias and provide an objective overview of information even if it contradicts your opinion. To produce a high-scoring synthesis essay, work on your analytical skills and use them to find evidence to defend your position.

If answering synthesis questions gives you trouble, use essay generator Aithor to generate sample essays, learn how to derive main information from source texts, create a plan, and express your thoughts concisely and eloquently.

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How to Write a Synthesis Essay: Your Guide From Start to Finish

Today, we're swamped with information, like reading 174 newspapers every day. It comes from all over—news, social media, science, and more. This flood might make you feel overwhelmed and lost in a sea of facts and opinions. But being able to make sense of it all is crucial.

This guide isn't just about handling all that info; it's about using it to write awesome essays. We'll show you step by step how to pick a topic and organize your essay. Let's dive in and learn how to turn scattered facts into powerful essays that really stand out.

What Is a Synthesis Essay

The synthesis essay is a powerful tool in writing. It's not just about gathering facts but about connecting them to make a clear and strong argument.

Writing a synthesis essay allows you to dive deep into ideas. You have to find similarities between different sources—like articles, studies, or arguments—and use them to tell a convincing story.

In today's world, where we're bombarded with information, synthesis essays are more important than ever. They let us explore how different ideas fit together and help us express our thoughts on complex topics. Whether you're writing about literature, science, history, or current events, a synthesis essay shows off your ability to analyze and understand a topic from all angles. And if you're struggling with this task, just ask us to ' write paper for me ,' and we'll handle your assignment for you.

Explanatory vs. Argumentative Synthesis Essays

In synthesis writing, there are two main types: explanatory and argumentative. Understanding these categories is key because they shape how you approach your essay.

Explanatory:

An explanatory synthesis essay does just what it says—it explains. These essays aim to give a balanced view of a topic by gathering information from different sources and presenting it clearly. They don't try to persuade; instead, they focus on providing information and making things easier to understand. They're like comprehensive summaries, breaking down complex ideas for a broader audience. These essays rely heavily on facts and expert opinions, avoiding personal bias.

Argumentative:

On the flip side, argumentative synthesis essays are all about persuasion. Their main goal is to take a stance on an issue and convince the reader. They gather information from various sources not only to present different views but also to build a strong argument. Argumentative essays aim to sway the reader's opinion by using gathered information as evidence. These essays express opinions and use rhetorical strategies to persuade.

And if you're keen on knowing how to write an informative essay , we've got you covered on that, too!

Synthesis Essay Structure

To craft a strong synthesis essay, you need a solid foundation. Here's a structured approach to help you nail it:

Introductory Paragraph:

• To kick things off, grab your reader's attention with a catchy hook or interesting fact. Give a bit of background info about your topic and the sources you'll be using, as it can help readers understand your topic better! Then, lay out your main argument in a clear thesis statement.

Body Paragraphs:

• Each paragraph should focus on a different aspect of your topic or source. Start with a topic sentence that links back to your thesis. Introduce the source you're discussing and highlight its main points. Also, using quotes, paraphrases, or summaries from your sources can make your arguments stronger.

Synthesis :

• This part is where your essay comes together. Look for common themes or differences among your sources. Use your analysis to build a strong argument. Don't forget to address any opposing viewpoints if they're relevant!

Conclusion :

• Wrap things up by restating your thesis and summarizing your main points. Explain why your argument is important and what it means in the bigger picture. End with a thought-provoking statement to leave a lasting impression.

References :

• Finally, don't forget to list all your sources properly using the right citation style, like MLA or APA. Do you know that different citation styles have different rules? So, make sure you follow the right one!

Choosing a Synthesis Essay Topic

Picking essay topics is just the beginning. To write a great synthesis essay, you need to carefully evaluate and connect different sources to build a strong argument or viewpoint. Here's a step-by-step infographic guide to help you choose the right synthesis essay topics wisely.

How to Write a Synthesis Essay with Easy Steps

Writing a synthesis essay is similar to a compare and contrast essay . It requires a methodical approach to blend information from different sources into a strong and persuasive argument. Here are some crucial steps and tips to help you along the way.

• Clarify Your Purpose: First, decide if you're writing an explanatory or argumentative synthesis essay. This choice will set the tone and direction for your essay.
• Source Selection and Analysis: Choose credible and relevant sources for your topic, balancing different types like articles, books, and websites. Analyze each source carefully, noting the main ideas and evidence presented.
• Formulate a Strong Thesis Statement: Create a clear and concise thesis statement that guides your essay. It should express your main argument or perspective.
• Structure Your Essay: Organize your essay with a clear synthesis essay outline, including an introduction, body paragraphs, and a conclusion. Each body paragraph should focus on a specific aspect of your topic.
• Employ Effective Transition Sentences: Use transition sentences to connect your ideas and paragraphs smoothly, ensuring a cohesive flow in your essay.
• Synthesize Information: Blend information from your sources within your paragraphs. Discuss how each source contributes to your thesis and highlight common themes or differences.
• Avoid Simple Summarization: Don't just summarize your sources—analyze them critically and use them to build your argument.
• Address Counterarguments (if applicable): Acknowledge opposing viewpoints and counter them with well-supported arguments, showing a deep understanding of the topic.
• Craft a Resolute Conclusion: Summarize your main points and restate your thesis in the conclusion. Emphasize the importance of your argument or insights, and end with a thought-provoking statement or call to action. ‍
• Revise and Proofread: Check your essay for clarity, coherence, and grammar mistakes. Ensure your citations are correct and follow the chosen citation style, like MLA or APA.

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Synthesis Essay Format

Choosing the right citation style can enhance the credibility and professionalism of your paper. The format of your synthesis paper depends on the specific guidelines given by your instructor. They usually fall into one of the popular styles: MLA, APA, or Chicago, each used in different academic fields.

1. MLA (Modern Language Association):

• Uses in-text citations with the author's last name and page number.
• Includes a 'Works Cited' page at the end listing all sources.
• Focuses on the author and publication date.
• Often used in humanities essays, research papers, and literary analyses.

2. APA (American Psychological Association):

• Uses in-text citations with the author's last name and publication date in parentheses.
• Includes a 'References' page listing all sources alphabetically.
• Emphasizes the publication date and scientific precision.
• Commonly used in research papers, scholarly articles, and scientific studies.

3. Chicago Style:

• Offers two documentation styles: Notes-Bibliography and Author-Date.
• Notes-Bibliography uses footnotes or endnotes for citations, while Author-Date uses in-text citations with a reference list.
• Suitable for various academic writing, including research papers and historical studies.
• Provides flexibility in formatting and citation methods, making it adaptable to different disciplines.

Synthesis Essay Example

Here are two examples of synthesis essays that demonstrate how to apply the synthesis process in real life. They explore interesting topics and offer practical guidance for mastering the art of writing this type of paper.

Synthesis Essay Tips

Crafting a strong synthesis essay requires careful planning and effective techniques. Here are five essential tips to help you write your best paper:

• Diverse Source Selection : Choose a range of reliable sources that offer different viewpoints on your topic. Make sure they're recent and relevant to your subject.
• Seamless Source Integration : Avoid just summarizing your sources. Instead, blend them into your essay by analyzing and comparing their ideas. Show how they connect to build your argument.
• Balanced Tone : Maintain an impartial tone in your writing, even if you have personal opinions. Synthesis essays require objectivity, so they present different viewpoints without bias.
• Focus on Synthesis : Remember, synthesis essays are about linking ideas, not just summarizing sources. Explore how your sources relate to each other to create a cohesive argument.
• Address Counterarguments : Like in persuasive essays topics , acknowledge opposing viewpoints and explain why your perspective is stronger. This demonstrates your understanding of the topic and adds depth to your argument.

Concluding Thoughts

When writing a synthesis essay, it's essential to pick trustworthy sources, blend them effectively to build your argument and stay objective. Use smooth transitions, address counterarguments thoughtfully, and focus on analyzing rather than just summarizing. By following these steps, you'll create essays that inform, persuade, and engage your readers!

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How Should You Conclude a Synthesis Essay?

Daniel Parker

is a seasoned educational writer focusing on scholarship guidance, research papers, and various forms of academic essays including reflective and narrative essays. His expertise also extends to detailed case studies. A scholar with a background in English Literature and Education, Daniel’s work on EssayPro blog aims to support students in achieving academic excellence and securing scholarships. His hobbies include reading classic literature and participating in academic forums.

is an expert in nursing and healthcare, with a strong background in history, law, and literature. Holding advanced degrees in nursing and public health, his analytical approach and comprehensive knowledge help students navigate complex topics. On EssayPro blog, Adam provides insightful articles on everything from historical analysis to the intricacies of healthcare policies. In his downtime, he enjoys historical documentaries and volunteering at local clinics.

Related Articles

Capstone Form and Style

Evidence-based arguments: synthesis, paraphrasing and synthesis.

Synthesis is important in scholarly writing as it is the combination of ideas on a given topic or subject area. Synthesis is different from summary. Summary consists of a brief description of one idea, piece of text, etc. Synthesis involves combining ideas together.

Summary: Overview of important general information in your own words and sentence structure. Paraphrase: Articulation of a specific passage or idea in your own words and sentence structure. Synthesis: New interpretation of summarized or paraphrased details in your own words and sentence structure.

In the capstone, writers should aim for synthesis in all areas of the document, especially the literature review. Synthesis combines paraphrased information, where the writer presents information from multiple sources. Synthesis demonstrates scholarship; it demonstrates an understanding of the literature and information, as well as the writer’s ability to connect ideas and develop an argument.

Example Paraphrase

From allan and zed (2012, p. 195).

Supervision, one practice in transactional leadership theory, is especially effective for small business owners. Improved retention not only contributes to an efficient workplace, but it promotes local commercial stability and cultural unity. Other management styles informed by transactional theory can also benefit communities.

Sample Paraphrase

Allan and Zed (2012) noted that supervision and other transactional leadership strategies provide advantages for small business owners and their surrounding communities.

This paraphrase DOES:

• include the main idea,
• summarize the key information using fewer words than the original text, and
• include a citation to credit the source.

Synthesis Language

Synthesis is achieved by comparing and contrasting paraphrased information on a given topic. Discussions of the literature should be focused not on study-by-study summaries (see the Creating a Literature Review Outline SMRTguide). Writers should begin by using comparison language (indicated in bold and highlighted text in the examples below) to combine ideas on a given topic:

• Keller (2012) found that X occurred. Likewise, Daal (2013) found that X occurred but also noted that the effects of X differed from those suggested by Keller (2012).
• Schwester (2013) reported results consistent with findings in Hill’s (2011) and Yao’s (2012) studies.
• Although Mehmad (2012) suggested X, O’Donnell (2013) recommended a different approach.

Again, the focus of synthesis is to combine ideas on a given topic and for the writer to use that to review the existing literature or support an overall argument (i.e., in the problem statement, rationale and justification for the method, etc.).

For more information and examples on synthesis, paragraph structure, and the MEAL Plan strategy for writing review additional Form and Style resources:

• SMRTguide on Reverse Outlining and the MEAL Plan
• SMRTguide on Prioritizing Parenthetical Citations
• Reading to Write
• Previous Page: Quoting
• Next Page: MEAL Plan
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57 Synthesis

Synthesis writing.

Although at its most basic level a synthesis involves combining two or more summaries, synthesis writing is more difficult than it might at first appear because this combining must be done in a meaningful way and the final essay must generally be thesis-driven.  In composition courses, “synthesis” commonly refers to writing about printed texts, drawing together particular themes or traits that you observe in those texts and organizing the material from each text according to those themes or traits.  Sometimes you may be asked to synthesize your own ideas, theory, or research with those of the texts you have been assigned. In your other college classes you’ll probably find yourself synthesizing  information from graphs and tables, pieces of music, and art works as well.  The  key  to any kind of synthesis is the same.

Synthesis in Every Day Life

Whenever you report to a friend the things several other friends have said about a film or CD you engage in synthesis.  People synthesize information naturally to help other see the connections between things they learn; for example, you have probably stored up a mental data bank of the various things you’ve heard about particular professors.  If your data bank contains several negative comments, you might synthesize that information and use it to help you decide not to take a class from that particular professor.  Synthesis is related to but not the same as classification, division, or comparison and contrast.  Instead of attending to categories or finding similarities and differences, synthesizing sources is a matter of pulling them together into some kind of harmony.  Synthesis searches for links between materials for the purpose of constructing a thesis or theory.

Synthesis Writing Outside of College

The basic research report (described below as a background synthesis) is very common in the business world.  Whether one is proposing to open a new store or expand a product line, the report that must inevitably be written will synthesize information and arrange it by topic rather than by source.  Whether you want to present information on child rearing to a new mother, or details about your town to a new resident, you’ll find yourself synthesizing too. And just as in college, the quality and usefulness of your synthesis will depend on your accuracy and organization.

Key Features of a Synthesis

(1)  It accurately reports information from the sources using different phrases and sentences; (2)  It is organized in such a way that readers can immediately see where the information from the sources overlap;. (3)  It makes sense of the sources and helps the reader understand them in greater depth.

The Background Synthesis

In the process of writing his or her background synthesis, the student explored the sources in a new way and become an expert on the topic.  Only when one has reached this degree of expertise is one ready to formulate a thesis.  Frequently writers of background synthesis papers develop a thesis before they have finished.  In the previous example, the student might notice that no two colleges seem to agree on what constitutes “co-curricular,” and decide to research this question in more depth, perhaps examining trends in higher education and offering an argument about what this newest trend seems to reveal.  [ More information on developing a research thesis .] The background synthesis requires that you bring  together background information on a topic and organize it by topic rather than by source.  Instructors often assign background syntheses at the early stages of the research process, before students have developed a thesis–and they can be helpful to students conducting large research projects even if they are not assigned.  In a background synthesis of  Internet information that could help prospective students select a college, for example, one paragraph might discuss residential life and synthesize brief descriptions of the kinds of things students might find out about living on campus (cited of course), another might discuss the academic program, again synthesizing information from the web sites of several colleges, while a third might synthesize information about co-curricular activities.  The completed paper would be a wonderful introduction to internet college searching.  It contains no thesis, but it does have a purpose:  to present the information that is out there in a helpful and logical way.

[See also “ Preparing to Write the Synthesis Essay ,” “ Writing the Synthesis Essa y,” and “ Revision .”]

A Thesis-driven Synthesis

On the other hand, all research papers are also synthesis papers in that they combine the information you have found in ways that help readers to see that information and the topic in question in a new way.  A research paper with a weak thesis (such as: “media images of women help to shape women’s sense of how they should look”) will organize its findings to show how this is so without having to spend much time discussing other arguments (in this case, other things that also help to shape women’s sense of how they should look).  A paper with a strong thesis (such as “the media is the single most important factor in shaping women’s sense of how they should look”) will spend more time discussing arguments that it rejects (in this case, each paragraph will show how the media is more influential than other Sometimes there is very little obvious difference between a background synthesis and a thesis-driven synthesis, especially if the paper answers the question “what information must we know in order to understand this topic, and why?”  The answer to that question forms the thesis of the resulting paper, but it may not be a particularly controversial thesis.  There may be some debate about what background information is required, or about why, but in most cases the papers will still seem more like a report than an argument.  The difference will be most visible in the topic sentences to each paragraph because instead of simply introducing the material for the paragraph that will follow, they will also link back to the thesis and assert that this information is essential because…

factors in that particular aspect of women’s sense of how they should look”).

[See also  thesis-driven research papers .] [See also “ Preparing to Write the Synthesis Essay ,” “ Writing the Synthesis Essa y,” and “ Revision .”]

A Synthesis of the Literature

Because each discipline has specific rules and expectations, you should consult your professor or a guide book for that specific discipline if you are asked to write a review of the literature and aren’t sure how to do it. In many upper level social sciences classes you may be asked to begin research papers with a synthesis of the sources.  This part of the paper which may be one paragraph or several pages depending on the length of the paper–is similar to the  background synthesis .  Your primary purpose is to show readers that you are familiar with the field and are thus qualified to offer your own opinions.  But your larger purpose is to show that in spite of all  this wonderful research, no one has addressed the problem in the way that you intend to in your paper.  This gives your synthesis a purpose, and even a thesis of sorts.

Preparing to write your Synthesis Essay

Sometimes the wording of your assignment will direct you to what sorts of themes or traits you should look for in your synthesis.  At other times, though, you may be assigned two or more sources and told to synthesize them.  In such cases you need to formulate your own purpose, and develop your own perspectives and interpretations.  A systematic preliminary comparison will help. Begin by summarizing briefly the points, themes, or traits that the texts have in common (you might find summary-outline notes  useful here).  Explore different ways to organize the information depending on what you find or what you want to demonstrate ( see above ).  You might find it helpful to make several different outlines or plans before you decide which to use.  As the most important aspect of a synthesis is its organization, you can’t spend too long on this aspect of your paper! Regardless of whether you are synthesizing information from prose sources, from laboratory data, or from tables and graphs, your preparation for the synthesis will very likely involve  comparison . It may involve  analysis , as well, along with classification, and division as you work on your organization.

Writing the Synthesis Essay

The introduction (usually one paragraph :

A synthesis essay should be organized so that others can understand the sources and evaluate your comprehension of them and their presentation of specific data, themes, etc. The following format works well:

• Contains a one-sentence statement that sums up the focus of your synthesis. 2.    Also introduces the texts to be synthesized: (i)  Gives the title of each source (following the citation guidelines of whatever style sheet you are using); (ii)  Provides the name of each author; (ii)  Sometimes also provides pertinent background information about the authors, about the texts to be summarized, or about the general topic from which the texts are drawn.

The body of a synthesis essay :

This should be organized by theme, point, similarity, or aspect of the topic.  Your organization will be determined by the assignment or by the patterns you see in the material you are synthesizing.  The organization is the most important part of a synthesis, so try out more than one format. Be sure that each paragraph : 1.     Begins with a sentence or phrase that informs readers of the topic of the paragraph; 2.     Includes information from more than one source; 3.     Clearly indicates which material comes from which source using lead in phrases and in-text citations.  [Beware of plagiarism:  Accidental plagiarism most often occurs when students are synthesizing sources and do not indicate where the synthesis ends and their own comments begin or vice verse.] 4.    Shows the similarities or differences between the different sources in ways that make the paper as informative as possible; 5.    Represents the texts fairly–even if that seems to weaken the paper! Look upon yourself as a synthesizing machine;  you are simply repeating what the source says, in fewer words and in your own words.  But the fact that you are using your own words does not mean that you are in anyway changing what the source says.

Conclusion :

When you have finished your paper, write a conclusion reminding readers of the most significant themes you have found and the ways they connect to the overall topic.  You may also want to suggest further research or comment on things that it was not possible for you to discuss in the paper. If you are writing a background synthesis, in some cases it may be appropriate for you to offer an interpretation of the material or take a position (thesis).  Check this option with your instructor before you write the final draft of your paper.

Checking your own writing or that of your peers

Read a peer’s synthesis and then answer the questions below.  The information provided will help the writer check that his or her paper does what he or she intended (for example, it is not necessarily wrong for a synthesis to include any of the writer’s opinions, indeed, in a thesis-driven paper this is essential; however, the reader must be able to identify which opinions originated with the writer of the paper and which came from the sources).

• What do you like best about your peer’s synthesis? (Why? How might he or she do more of it?);
• Is it clear what is being synthesized? (i.e.: Did your peer list the source(s), and cite it/them correctly?);
• Is it always clear which source your peer is talking about at any given moment? (Mark any places where it is not clear);
• Is the thesis of each original text clear in the synthesis? (Write out what you think each thesis is);
• did you identify the same theses as your peer? (If not, how do they differ?);
• did your peer miss any key points from his or her synthesis? (If so, what are they?);
• did your peer include any of his own opinions in his or her synthesis? (If so, what are they?);
• Where there any points in the synthesis where you were lost because a transition was missing or material seems to have been omitted?  (If so, where and how might it be fixed?);
• What is the organizational structure of the synthesis essay? (It might help to draw a plan/diagram);
• Does this structure work?  (If not, how might your peer revise it?);
• How is each paragraph structured?  (It might help to draw a plan/diagram);
• Is this method effective?  (If not, how should your peer revise?);
• Was there a mechanical, grammatical, or spelling error that annoyed you as you read the paper?  (If so, how could the author fix it?  Did you notice this error occurring more than once?)   Do not comment on every typographical or other error you see.  It is a waste of time to carefully edit a paper before it is revised!
• What other advice do you have for the author of this paper?

Write What Matters Copyright © 2020 by Liza Long; Amy Minervini; and Joel Gladd is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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When you look for areas where your sources agree or disagree and try to draw broader conclusions about your topic based on what your sources say, you are engaging in synthesis. Writing a research paper usually requires synthesizing the available sources in order to provide new insight or a different perspective into your particular topic (as opposed to simply restating what each individual source says about your research topic).

Note that synthesizing is not the same as summarizing.  

• A summary restates the information in one or more sources without providing new insight or reaching new conclusions.
• A synthesis draws on multiple sources to reach a broader conclusion.

There are two types of syntheses: explanatory syntheses and argumentative syntheses . Explanatory syntheses seek to bring sources together to explain a perspective and the reasoning behind it. Argumentative syntheses seek to bring sources together to make an argument. Both types of synthesis involve looking for relationships between sources and drawing conclusions.

In order to successfully synthesize your sources, you might begin by grouping your sources by topic and looking for connections. For example, if you were researching the pros and cons of encouraging healthy eating in children, you would want to separate your sources to find which ones agree with each other and which ones disagree.

After you have a good idea of what your sources are saying, you want to construct your body paragraphs in a way that acknowledges different sources and highlights where you can draw new conclusions.

As you continue synthesizing, here are a few points to remember:

• Don’t force a relationship between sources if there isn’t one. Not all of your sources have to complement one another.
• Do your best to highlight the relationships between sources in very clear ways.
• Don’t ignore any outliers in your research. It’s important to take note of every perspective (even those that disagree with your broader conclusions).

Example Syntheses

Below are two examples of synthesis: one where synthesis is NOT utilized well, and one where it is.

Parents are always trying to find ways to encourage healthy eating in their children. Elena Pearl Ben-Joseph, a doctor and writer for KidsHealth , encourages parents to be role models for their children by not dieting or vocalizing concerns about their body image. The first popular diet began in 1863. William Banting named it the “Banting” diet after himself, and it consisted of eating fruits, vegetables, meat, and dry wine. Despite the fact that dieting has been around for over a hundred and fifty years, parents should not diet because it hinders children’s understanding of healthy eating.

In this sample paragraph, the paragraph begins with one idea then drastically shifts to another. Rather than comparing the sources, the author simply describes their content. This leads the paragraph to veer in an different direction at the end, and it prevents the paragraph from expressing any strong arguments or conclusions.

An example of a stronger synthesis can be found below.

Parents are always trying to find ways to encourage healthy eating in their children. Different scientists and educators have different strategies for promoting a well-rounded diet while still encouraging body positivity in children. David R. Just and Joseph Price suggest in their article “Using Incentives to Encourage Healthy Eating in Children” that children are more likely to eat fruits and vegetables if they are given a reward (855-856). Similarly, Elena Pearl Ben-Joseph, a doctor and writer for Kids Health , encourages parents to be role models for their children. She states that “parents who are always dieting or complaining about their bodies may foster these same negative feelings in their kids. Try to keep a positive approach about food” (Ben-Joseph). Martha J. Nepper and Weiwen Chai support Ben-Joseph’s suggestions in their article “Parents’ Barriers and Strategies to Promote Healthy Eating among School-age Children.” Nepper and Chai note, “Parents felt that patience, consistency, educating themselves on proper nutrition, and having more healthy foods available in the home were important strategies when developing healthy eating habits for their children.” By following some of these ideas, parents can help their children develop healthy eating habits while still maintaining body positivity.

In this example, the author puts different sources in conversation with one another. Rather than simply describing the content of the sources in order, the author uses transitions (like "similarly") and makes the relationship between the sources evident.

Persuasive Writing In Three Steps: Thesis, Antithesis, Synthesis

April 14, 2021 by Ryan Law in

Great writing persuades. It persuades the reader that your product is right for them, that your process achieves the outcome they desire, that your opinion supersedes all other opinions. But spend an hour clicking around the internet and you’ll quickly realise that most content is passive, presenting facts and ideas without context or structure. The reader must connect the dots and create a convincing argument from the raw material presented to them. They rarely do, and for good reason: It’s hard work. The onus of persuasion falls on the writer, not the reader. Persuasive communication is a timeless challenge with an ancient solution. Zeno of Elea cracked it in the 5th century B.C. Georg Hegel gave it a lick of paint in the 1800s. You can apply it to your writing in three simple steps: thesis, antithesis, synthesis.

Use Dialectic to Find Logical Bedrock

“ Dialectic ” is a complicated-sounding idea with a simple meaning: It’s a structured process for taking two seemingly contradictory viewpoints and, through reasoned discussion, reaching a satisfactory conclusion. Over centuries of use the term has been burdened with the baggage of philosophy and academia. But at its heart, dialectics reflects a process similar to every spirited conversation or debate humans have ever had:

• Person A presents an idea: “We should travel to the Eastern waterhole because it’s closest to camp.”
• Person B disagrees and shares a counterargument: “I saw wolf prints on the Eastern trail, so we should go to the Western waterhole instead.”
• Person A responds to the counterargument , either disproving it or modifying their own stance to accommodate the criticism: “I saw those same wolf prints, but our party is large enough that the wolves won’t risk an attack.”
• Person B responds in a similar vein: “Ordinarily that would be true, but half of our party had dysentery last week so we’re not at full strength.”
• Person A responds: “They got dysentery from drinking at the Western waterhole.”

This process continues until conversational bedrock is reached: an idea that both parties understand and agree to, helped by the fact they’ve both been a part of the process that shaped it.

Dialectic is intended to help draw closer to the “truth” of an argument, tempering any viewpoint by working through and resolving its flaws. This same process can also be used to persuade.

Create Inevitability with Thesis, Antithesis, Synthesis

The philosopher Georg Hegel is most famous for popularizing a type of dialectics that is particularly well-suited to writing: thesis, antithesis, synthesis (also known, unsurprisingly, as Hegelian Dialectic ).

• Thesis: Present the status quo, the viewpoint that is currently accepted and widely held.
• Antithesis: Articulate the problems with the thesis. (Hegel also called this phase “the negative.”)
• Synthesis: Share a new viewpoint (a modified thesis) that resolves the problems.

Hegel’s method focused less on the search for absolute truth and more on replacing old ideas with newer, more sophisticated versions . That, in a nutshell, is the same objective as much of content marketing (and particularly thought leadership content ): We’re persuading the reader that our product, processes, and ideas are better and more useful than the “old” way of doing things. Thesis, antithesis, synthesis (or TAS) is a persuasive writing structure because it:

• Reduces complex arguments into a simple three-act structure. Complicated, nuanced arguments are simplified into a clear, concise format that anyone can follow. This simplification reflects well on the author: It takes mastery of a topic to explain it in it the simplest terms.
• Presents a balanced argument by “steelmanning” the best objection. Strong, one-sided arguments can trigger reactance in the reader: They don’t want to feel duped. TAS gives voice to their doubts, addressing their best objection and “giv[ing] readers the chance to entertain the other side, making them feel as though they have come to an objective conclusion.”
• Creates a sense of inevitability. Like a story building to a satisfying conclusion, articles written with TAS take the reader on a structured, logical journey that culminates in precisely the viewpoint we wish to advocate for. Doubts are voiced, ideas challenged, and the conclusion reached feels more valid and concrete as a result.

There are two main ways to apply TAS to your writing: Use it beef up your introductions, or apply it to your article’s entire structure.

Writing Article Introductions with TAS

Take a moment to scroll back to the top of this article. If I’ve done my job correctly, you’ll notice a now familiar formula staring back at you: The first three paragraphs are built around Hegel’s thesis, antithesis, synthesis structure. Here’s what the introduction looked like during the outlining process . The first paragraph shares the thesis, the accepted idea that great writing should be persuasive:

Next up, the antithesis introduces a complicating idea, explaining why most content marketing isn’t all that persuasive:

Finally, the synthesis shares a new idea that serves to reconcile the two previous paragraphs: Content can be made persuasive by using the thesis, antithesis, synthesis framework. The meat of the article is then focused on the nitty-gritty of the synthesis.

Introductions are hard, but thesis, antithesis, synthesis offers a simple way to write consistently persuasive opening copy. In the space of three short paragraphs, the article’s key ideas are shared , the entire argument is summarised, and—hopefully—the reader is hooked.

Best of all, most articles—whether how-to’s, thought leadership content, or even list content—can benefit from Hegelian Dialectic , for the simple reason that every article introduction should be persuasive enough to encourage the reader to stick around.

Structuring Entire Articles with TAS

Harder, but most persuasive, is to use thesis, antithesis, synthesis to structure your entire article. This works best for thought leadership content. Here, your primary objective is to advocate for a new idea and disprove the old, tired way of thinking—exactly the use case Hegel intended for his dialectic. It’s less useful for content that explores and illustrates a process, because the primary objective is to show the reader how to do something (like this article—otherwise, I would have written the whole darn thing using the framework). Arjun Sethi’s article The Hive is the New Network is a great example.

The article’s primary purpose is to explain why the “old” model of social networks is outmoded and offer a newer, better framework. (It would be equally valid—but less punchy—to publish this with the title “ Why the Hive is the New Network.”) The thesis, antithesis, synthesis structure shapes the entire article:

• Thesis: Facebook, Twitter, and Instagram grew by creating networks “that brought existing real-world relationships online.”
• Antithesis: As these networks grow, the less useful they become, skewing towards bots, “celebrity, meme and business accounts.”
• Synthesis: To survive continued growth, these networks need to embrace a new structure and become hives.

With the argument established, the vast majority of the article is focused on synthesis. After all, it requires little elaboration to share the status quo in a particular situation, and it’s relatively easy to point out the problems with a given idea. The synthesis—the solution that needs to reconcile both thesis and antithesis—is the hardest part to tackle and requires the greatest word count. Throughout the article, Arjun is systematically addressing the “best objections” to his theory and demonstrating why the “Hive” is the best solution:

• Antithesis: Why now? Why didn’t Hives emerge in the first place?
• Thesis: We were limited by technology, but today, we have the necessary infrastructure: “We’re no longer limited to a broadcast radio model, where one signal is received by many nodes. ...We sync with each other instantaneously, and all the time.”
• Antithesis: If the Hive is so smart, why aren’t our brightest and best companies already embracing it?
• Thesis: They are, and autonomous cars are a perfect example: “Why are all these vastly different companies converging on the autonomous car? That’s because for these companies, it’s about platform and hive, not just about roads without drivers.”

It takes bravery to tackle objections head-on and an innate understanding of the subject matter to even identify objections in the first place, but the effort is worthwhile. The end result is a structured journey through the arguments for and against the “Hive,” with the reader eventually reaching the same conclusion as the author: that “Hives” are superior to traditional networks.

Destination: Persuasion

Persuasion isn’t about cajoling or coercing the reader. Statistics and anecdotes alone aren’t all that persuasive. Simply sharing a new idea and hoping that it will trigger an about-turn in the reader’s beliefs is wishful thinking. Instead, you should take the reader on a journey—the same journey you travelled to arrive at your newfound beliefs, whether it’s about the superiority of your product or the zeitgeist-changing trend that’s about to break. Hegelian Dialectic—thesis, antithesis, synthesis— is a structured process for doing precisely that. It contextualises your ideas and explains why they matter. It challenges the idea and strengthens it in the process. Using centuries-old processes, it nudges the 21st-century reader onto a well-worn path that takes them exactly where they need to go.

Ryan is the Content Director at Ahrefs and former CMO of Animalz.

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Literature Review Survival Library Guide: Thesis, antithesis and synthesis

• What is a literature review?
• Thesis, antithesis and synthesis
• 1. Choose your topic
• 2. Collect relevant material
• 3. Read/Skim articles
• 4. Group articles by themes
• 5. Use citation databases
• 6. Find agreement & disagreement
• Review Articles - A new option on Google Scholar
• How To Follow References
• Newspaper archives
• Aditi's Humanities Referencing Style Guide
• Referencing and RefWorks
• New-version RefWorks Demo
• Tracking Your Academic Footprint This link opens in a new window
• Finding Seminal Authors and Mapping the Shape of the Literature
• Types of Literature Review, including "Systematic Reviews in the Social Sciences: A Practical Guide"
• Research Data Management
• Tamzyn Suleiman's guide to Systematic Reviews
• Danielle Abrahamse's Search String Design and Search Template

Thesis, antithesis, synthesis

The classic pattern of academic arguments is:

Thesis, antithesis, synthesis.

An Idea (Thesis) is proposed, an opposing Idea (Antithesis) is proposed, and a revised Idea incorporating (Synthesis) the opposing Idea is arrived at. This revised idea sometimes sparks another opposing idea, another synthesis, and so on…

If you can show this pattern at work in your literature review, and, above all, if you can suggest a new synthesis of two opposing views, or demolish one of the opposing views, then you are almost certainly on the right track.

Next topic: Step 1: Choose your topic

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Hegel’s Dialectics

“Dialectics” is a term used to describe a method of philosophical argument that involves some sort of contradictory process between opposing sides. In what is perhaps the most classic version of “dialectics”, the ancient Greek philosopher, Plato (see entry on Plato ), for instance, presented his philosophical argument as a back-and-forth dialogue or debate, generally between the character of Socrates, on one side, and some person or group of people to whom Socrates was talking (his interlocutors), on the other. In the course of the dialogues, Socrates’ interlocutors propose definitions of philosophical concepts or express views that Socrates challenges or opposes. The back-and-forth debate between opposing sides produces a kind of linear progression or evolution in philosophical views or positions: as the dialogues go along, Socrates’ interlocutors change or refine their views in response to Socrates’ challenges and come to adopt more sophisticated views. The back-and-forth dialectic between Socrates and his interlocutors thus becomes Plato’s way of arguing against the earlier, less sophisticated views or positions and for the more sophisticated ones later.

“Hegel’s dialectics” refers to the particular dialectical method of argument employed by the 19th Century German philosopher, G.W.F. Hegel (see entry on Hegel ), which, like other “dialectical” methods, relies on a contradictory process between opposing sides. Whereas Plato’s “opposing sides” were people (Socrates and his interlocutors), however, what the “opposing sides” are in Hegel’s work depends on the subject matter he discusses. In his work on logic, for instance, the “opposing sides” are different definitions of logical concepts that are opposed to one another. In the Phenomenology of Spirit , which presents Hegel’s epistemology or philosophy of knowledge, the “opposing sides” are different definitions of consciousness and of the object that consciousness is aware of or claims to know. As in Plato’s dialogues, a contradictory process between “opposing sides” in Hegel’s dialectics leads to a linear evolution or development from less sophisticated definitions or views to more sophisticated ones later. The dialectical process thus constitutes Hegel’s method for arguing against the earlier, less sophisticated definitions or views and for the more sophisticated ones later. Hegel regarded this dialectical method or “speculative mode of cognition” (PR §10) as the hallmark of his philosophy and used the same method in the Phenomenology of Spirit [PhG], as well as in all of the mature works he published later—the entire Encyclopaedia of Philosophical Sciences (including, as its first part, the “Lesser Logic” or the Encyclopaedia Logic [EL]), the Science of Logic [SL], and the Philosophy of Right [PR].

Note that, although Hegel acknowledged that his dialectical method was part of a philosophical tradition stretching back to Plato, he criticized Plato’s version of dialectics. He argued that Plato’s dialectics deals only with limited philosophical claims and is unable to get beyond skepticism or nothingness (SL-M 55–6; SL-dG 34–5; PR, Remark to §31). According to the logic of a traditional reductio ad absurdum argument, if the premises of an argument lead to a contradiction, we must conclude that the premises are false—which leaves us with no premises or with nothing. We must then wait around for new premises to spring up arbitrarily from somewhere else, and then see whether those new premises put us back into nothingness or emptiness once again, if they, too, lead to a contradiction. Because Hegel believed that reason necessarily generates contradictions, as we will see, he thought new premises will indeed produce further contradictions. As he puts the argument, then,

the scepticism that ends up with the bare abstraction of nothingness or emptiness cannot get any further from there, but must wait to see whether something new comes along and what it is, in order to throw it too into the same empty abyss. (PhG-M §79)

Hegel argues that, because Plato’s dialectics cannot get beyond arbitrariness and skepticism, it generates only approximate truths, and falls short of being a genuine science (SL-M 55–6; SL-dG 34–5; PR, Remark to §31; cf. EL Remark to §81). The following sections examine Hegel’s dialectics as well as these issues in more detail.

1. Hegel’s description of his dialectical method

2. applying hegel’s dialectical method to his arguments, 3. why does hegel use dialectics, 4. is hegel’s dialectical method logical, 5. syntactic patterns and special terminology in hegel’s dialectics, english translations of key texts by hegel, english translations of other primary sources, secondary literature, other internet resources, related entries.

Hegel provides the most extensive, general account of his dialectical method in Part I of his Encyclopaedia of Philosophical Sciences , which is often called the Encyclopaedia Logic [EL]. The form or presentation of logic, he says, has three sides or moments (EL §79). These sides are not parts of logic, but, rather, moments of “every concept”, as well as “of everything true in general” (EL Remark to §79; we will see why Hegel thought dialectics is in everything in section 3 ). The first moment—the moment of the understanding—is the moment of fixity, in which concepts or forms have a seemingly stable definition or determination (EL §80).

The second moment—the “ dialectical ” (EL §§79, 81) or “ negatively rational ” (EL §79) moment—is the moment of instability. In this moment, a one-sidedness or restrictedness (EL Remark to §81) in the determination from the moment of understanding comes to the fore, and the determination that was fixed in the first moment passes into its opposite (EL §81). Hegel describes this process as a process of “self-sublation” (EL §81). The English verb “to sublate” translates Hegel’s technical use of the German verb aufheben , which is a crucial concept in his dialectical method. Hegel says that aufheben has a doubled meaning: it means both to cancel (or negate) and to preserve at the same time (PhG §113; SL-M 107; SL-dG 81–2; cf. EL the Addition to §95). The moment of understanding sublates itself because its own character or nature—its one-sidedness or restrictedness—destabilizes its definition and leads it to pass into its opposite. The dialectical moment thus involves a process of self -sublation, or a process in which the determination from the moment of understanding sublates itself , or both cancels and preserves itself , as it pushes on to or passes into its opposite.

The third moment—the “ speculative ” or “ positively rational ” (EL §§79, 82) moment—grasps the unity of the opposition between the first two determinations, or is the positive result of the dissolution or transition of those determinations (EL §82 and Remark to §82). Here, Hegel rejects the traditional, reductio ad absurdum argument, which says that when the premises of an argument lead to a contradiction, then the premises must be discarded altogether, leaving nothing. As Hegel suggests in the Phenomenology , such an argument

is just the skepticism which only ever sees pure nothingness in its result and abstracts from the fact that this nothingness is specifically the nothingness of that from which it results . (PhG-M §79)

Although the speculative moment negates the contradiction, it is a determinate or defined nothingness because it is the result of a specific process. There is something particular about the determination in the moment of understanding—a specific weakness, or some specific aspect that was ignored in its one-sidedness or restrictedness—that leads it to fall apart in the dialectical moment. The speculative moment has a definition, determination or content because it grows out of and unifies the particular character of those earlier determinations, or is “a unity of distinct determinations ” (EL Remark to §82). The speculative moment is thus “truly not empty, abstract nothing , but the negation of certain determinations ” (EL-GSH §82). When the result “is taken as the result of that from which it emerges”, Hegel says, then it is “in fact, the true result; in that case it is itself a determinate nothingness, one which has a content” (PhG-M §79). As he also puts it, “the result is conceived as it is in truth, namely, as a determinate negation [ bestimmte Negation]; a new form has thereby immediately arisen” (PhG-M §79). Or, as he says, “[b]ecause the result, the negation, is a determinate negation [bestimmte Negation ], it has a content ” (SL-dG 33; cf. SL-M 54). Hegel’s claim in both the Phenomenology and the Science of Logic that his philosophy relies on a process of “ determinate negation [ bestimmte Negation]” has sometimes led scholars to describe his dialectics as a method or doctrine of “determinate negation” (see entry on Hegel, section on Science of Logic ; cf. Rosen 1982: 30; Stewart 1996, 2000: 41–3; Winfield 1990: 56).

There are several features of this account that Hegel thinks raise his dialectical method above the arbitrariness of Plato’s dialectics to the level of a genuine science. First, because the determinations in the moment of understanding sublate themselves , Hegel’s dialectics does not require some new idea to show up arbitrarily. Instead, the movement to new determinations is driven by the nature of the earlier determinations and so “comes about on its own accord” (PhG-P §79). Indeed, for Hegel, the movement is driven by necessity (see, e.g., EL Remarks to §§12, 42, 81, 87, 88; PhG §79). The natures of the determinations themselves drive or force them to pass into their opposites. This sense of necessity —the idea that the method involves being forced from earlier moments to later ones—leads Hegel to regard his dialectics as a kind of logic . As he says in the Phenomenology , the method’s “proper exposition belongs to logic” (PhG-M §48). Necessity—the sense of being driven or forced to conclusions—is the hallmark of “logic” in Western philosophy.

Second, because the form or determination that arises is the result of the self-sublation of the determination from the moment of understanding, there is no need for some new idea to show up from the outside. Instead, the transition to the new determination or form is necessitated by earlier moments and hence grows out of the process itself. Unlike in Plato’s arbitrary dialectics, then—which must wait around until some other idea comes in from the outside—in Hegel’s dialectics “nothing extraneous is introduced”, as he says (SL-M 54; cf. SL-dG 33). His dialectics is driven by the nature, immanence or “inwardness” of its own content (SL-M 54; cf. SL-dG 33; cf. PR §31). As he puts it, dialectics is “the principle through which alone immanent coherence and necessity enter into the content of science” (EL-GSH Remark to §81).

Third, because later determinations “sublate” earlier determinations, the earlier determinations are not completely cancelled or negated. On the contrary, the earlier determinations are preserved in the sense that they remain in effect within the later determinations. When Being-for-itself, for instance, is introduced in the logic as the first concept of ideality or universality and is defined by embracing a set of “something-others”, Being-for-itself replaces the something-others as the new concept, but those something-others remain active within the definition of the concept of Being-for-itself. The something-others must continue to do the work of picking out individual somethings before the concept of Being-for-itself can have its own definition as the concept that gathers them up. Being-for-itself replaces the something-others, but it also preserves them, because its definition still requires them to do their work of picking out individual somethings (EL §§95–6).

The concept of “apple”, for example, as a Being-for-itself, would be defined by gathering up individual “somethings” that are the same as one another (as apples). Each individual apple can be what it is (as an apple) only in relation to an “other” that is the same “something” that it is (i.e., an apple). That is the one-sidedness or restrictedness that leads each “something” to pass into its “other” or opposite. The “somethings” are thus both “something-others”. Moreover, their defining processes lead to an endless process of passing back and forth into one another: one “something” can be what it is (as an apple) only in relation to another “something” that is the same as it is, which, in turn, can be what it is (an apple) only in relation to the other “something” that is the same as it is, and so on, back and forth, endlessly (cf. EL §95). The concept of “apple”, as a Being-for-itself, stops that endless, passing-over process by embracing or including the individual something-others (the apples) in its content. It grasps or captures their character or quality as apples . But the “something-others” must do their work of picking out and separating those individual items (the apples) before the concept of “apple”—as the Being-for-itself—can gather them up for its own definition. We can picture the concept of Being-for-itself like this:

Later concepts thus replace, but also preserve, earlier concepts.

Fourth, later concepts both determine and also surpass the limits or finitude of earlier concepts. Earlier determinations sublate themselves —they pass into their others because of some weakness, one-sidedness or restrictedness in their own definitions. There are thus limitations in each of the determinations that lead them to pass into their opposites. As Hegel says, “that is what everything finite is: its own sublation” (EL-GSH Remark to §81). Later determinations define the finiteness of the earlier determinations. From the point of view of the concept of Being-for-itself, for instance, the concept of a “something-other” is limited or finite: although the something-others are supposed to be the same as one another, the character of their sameness (e.g., as apples) is captured only from above, by the higher-level, more universal concept of Being-for-itself. Being-for-itself reveals the limitations of the concept of a “something-other”. It also rises above those limitations, since it can do something that the concept of a something-other cannot do. Dialectics thus allows us to get beyond the finite to the universal. As Hegel puts it, “all genuine, nonexternal elevation above the finite is to be found in this principle [of dialectics]” (EL-GSH Remark to §81).

Fifth, because the determination in the speculative moment grasps the unity of the first two moments, Hegel’s dialectical method leads to concepts or forms that are increasingly comprehensive and universal. As Hegel puts it, the result of the dialectical process

is a new concept but one higher and richer than the preceding—richer because it negates or opposes the preceding and therefore contains it, and it contains even more than that, for it is the unity of itself and its opposite. (SL-dG 33; cf. SL-M 54)

Like Being-for-itself, later concepts are more universal because they unify or are built out of earlier determinations, and include those earlier determinations as part of their definitions. Indeed, many other concepts or determinations can also be depicted as literally surrounding earlier ones (cf. Maybee 2009: 73, 100, 112, 156, 193, 214, 221, 235, 458).

Finally, because the dialectical process leads to increasing comprehensiveness and universality, it ultimately produces a complete series, or drives “to completion” (SL-dG 33; cf. SL-M 54; PhG §79). Dialectics drives to the “Absolute”, to use Hegel’s term, which is the last, final, and completely all-encompassing or unconditioned concept or form in the relevant subject matter under discussion (logic, phenomenology, ethics/politics and so on). The “Absolute” concept or form is unconditioned because its definition or determination contains all the other concepts or forms that were developed earlier in the dialectical process for that subject matter. Moreover, because the process develops necessarily and comprehensively through each concept, form or determination, there are no determinations that are left out of the process. There are therefore no left-over concepts or forms—concepts or forms outside of the “Absolute”—that might “condition” or define it. The “Absolute” is thus unconditioned because it contains all of the conditions in its content, and is not conditioned by anything else outside of it. This Absolute is the highest concept or form of universality for that subject matter. It is the thought or concept of the whole conceptual system for the relevant subject matter. We can picture the Absolute Idea (EL §236), for instance—which is the “Absolute” for logic—as an oval that is filled up with and surrounds numerous, embedded rings of smaller ovals and circles, which represent all of the earlier and less universal determinations from the logical development (cf. Maybee 2009: 30, 600):

Since the “Absolute” concepts for each subject matter lead into one another, when they are taken together, they constitute Hegel’s entire philosophical system, which, as Hegel says, “presents itself therefore as a circle of circles” (EL-GSH §15). We can picture the entire system like this (cf. Maybee 2009: 29):

Together, Hegel believes, these characteristics make his dialectical method genuinely scientific. As he says, “the dialectical constitutes the moving soul of scientific progression” (EL-GSH Remark to §81). He acknowledges that a description of the method can be more or less complete and detailed, but because the method or progression is driven only by the subject matter itself, this dialectical method is the “only true method” (SL-M 54; SL-dG 33).

So far, we have seen how Hegel describes his dialectical method, but we have yet to see how we might read this method into the arguments he offers in his works. Scholars often use the first three stages of the logic as the “textbook example” (Forster 1993: 133) to illustrate how Hegel’s dialectical method should be applied to his arguments. The logic begins with the simple and immediate concept of pure Being, which is said to illustrate the moment of the understanding. We can think of Being here as a concept of pure presence. It is not mediated by any other concept—or is not defined in relation to any other concept—and so is undetermined or has no further determination (EL §86; SL-M 82; SL-dG 59). It asserts bare presence, but what that presence is like has no further determination. Because the thought of pure Being is undetermined and so is a pure abstraction, however, it is really no different from the assertion of pure negation or the absolutely negative (EL §87). It is therefore equally a Nothing (SL-M 82; SL-dG 59). Being’s lack of determination thus leads it to sublate itself and pass into the concept of Nothing (EL §87; SL-M 82; SL-dG 59), which illustrates the dialectical moment.

But if we focus for a moment on the definitions of Being and Nothing themselves, their definitions have the same content. Indeed, both are undetermined, so they have the same kind of undefined content. The only difference between them is “something merely meant ” (EL-GSH Remark to §87), namely, that Being is an undefined content, taken as or meant to be presence, while Nothing is an undefined content, taken as or meant to be absence. The third concept of the logic—which is used to illustrate the speculative moment—unifies the first two moments by capturing the positive result of—or the conclusion that we can draw from—the opposition between the first two moments. The concept of Becoming is the thought of an undefined content, taken as presence (Being) and then taken as absence (Nothing), or taken as absence (Nothing) and then taken as presence (Being). To Become is to go from Being to Nothing or from Nothing to Being, or is, as Hegel puts it, “the immediate vanishing of the one in the other” (SL-M 83; cf. SL-dG 60). The contradiction between Being and Nothing thus is not a reductio ad absurdum , or does not lead to the rejection of both concepts and hence to nothingness—as Hegel had said Plato’s dialectics does (SL-M 55–6; SL-dG 34–5)—but leads to a positive result, namely, to the introduction of a new concept—the synthesis—which unifies the two, earlier, opposed concepts.

We can also use the textbook Being-Nothing-Becoming example to illustrate Hegel’s concept of aufheben (to sublate), which, as we saw, means to cancel (or negate) and to preserve at the same time. Hegel says that the concept of Becoming sublates the concepts of Being and Nothing (SL-M 105; SL-dG 80). Becoming cancels or negates Being and Nothing because it is a new concept that replaces the earlier concepts; but it also preserves Being and Nothing because it relies on those earlier concepts for its own definition. Indeed, it is the first concrete concept in the logic. Unlike Being and Nothing, which had no definition or determination as concepts themselves and so were merely abstract (SL-M 82–3; SL-dG 59–60; cf. EL Addition to §88), Becoming is a “ determinate unity in which there is both Being and Nothing” (SL-M 105; cf. SL-dG 80). Becoming succeeds in having a definition or determination because it is defined by, or piggy-backs on, the concepts of Being and Nothing.

This “textbook” Being-Nothing-Becoming example is closely connected to the traditional idea that Hegel’s dialectics follows a thesis-antithesis-synthesis pattern, which, when applied to the logic, means that one concept is introduced as a “thesis” or positive concept, which then develops into a second concept that negates or is opposed to the first or is its “antithesis”, which in turn leads to a third concept, the “synthesis”, that unifies the first two (see, e.g., McTaggert 1964 [1910]: 3–4; Mure 1950: 302; Stace, 1955 [1924]: 90–3, 125–6; Kosek 1972: 243; E. Harris 1983: 93–7; Singer 1983: 77–79). Versions of this interpretation of Hegel’s dialectics continue to have currency (e.g., Forster 1993: 131; Stewart 2000: 39, 55; Fritzman 2014: 3–5). On this reading, Being is the positive moment or thesis, Nothing is the negative moment or antithesis, and Becoming is the moment of aufheben or synthesis—the concept that cancels and preserves, or unifies and combines, Being and Nothing.

We must be careful, however, not to apply this textbook example too dogmatically to the rest of Hegel’s logic or to his dialectical method more generally (for a classic criticism of the thesis-antithesis-synthesis reading of Hegel’s dialectics, see Mueller 1958). There are other places where this general pattern might describe some of the transitions from stage to stage, but there are many more places where the development does not seem to fit this pattern very well. One place where the pattern seems to hold, for instance, is where the Measure (EL §107)—as the combination of Quality and Quantity—transitions into the Measureless (EL §107), which is opposed to it, which then in turn transitions into Essence, which is the unity or combination of the two earlier sides (EL §111). This series of transitions could be said to follow the general pattern captured by the “textbook example”: Measure would be the moment of the understanding or thesis, the Measureless would be the dialectical moment or antithesis, and Essence would be the speculative moment or synthesis that unifies the two earlier moments. However, before the transition to Essence takes place, the Measureless itself is redefined as a Measure (EL §109)—undercutting a precise parallel with the textbook Being-Nothing-Becoming example, since the transition from Measure to Essence would not follow a Measure-Measureless-Essence pattern, but rather a Measure-(Measureless?)-Measure-Essence pattern.

Other sections of Hegel’s philosophy do not fit the triadic, textbook example of Being-Nothing-Becoming at all, as even interpreters who have supported the traditional reading of Hegel’s dialectics have noted. After using the Being-Nothing-Becoming example to argue that Hegel’s dialectical method consists of “triads” whose members “are called the thesis, antithesis, synthesis” (Stace 1955 [1924]: 93), W.T. Stace, for instance, goes on to warn us that Hegel does not succeed in applying this pattern throughout the philosophical system. It is hard to see, Stace says, how the middle term of some of Hegel’s triads are the opposites or antitheses of the first term, “and there are even ‘triads’ which contain four terms!” (Stace 1955 [1924]: 97). As a matter of fact, one section of Hegel’s logic—the section on Cognition—violates the thesis-antithesis-synthesis pattern because it has only two sub-divisions, rather than three. “The triad is incomplete”, Stace complains. “There is no third. Hegel here abandons the triadic method. Nor is any explanation of his having done so forthcoming” (Stace 1955 [1924]: 286; cf. McTaggart 1964 [1910]: 292).

Interpreters have offered various solutions to the complaint that Hegel’s dialectics sometimes seems to violate the triadic form. Some scholars apply the triadic form fairly loosely across several stages (e.g. Burbidge 1981: 43–5; Taylor 1975: 229–30). Others have applied Hegel’s triadic method to whole sections of his philosophy, rather than to individual stages. For G.R.G. Mure, for instance, the section on Cognition fits neatly into a triadic, thesis-antithesis-synthesis account of dialectics because the whole section is itself the antithesis of the previous section of Hegel’s logic, the section on Life (Mure 1950: 270). Mure argues that Hegel’s triadic form is easier to discern the more broadly we apply it. “The triadic form appears on many scales”, he says, “and the larger the scale we consider the more obvious it is” (Mure 1950: 302).

Scholars who interpret Hegel’s description of dialectics on a smaller scale—as an account of how to get from stage to stage—have also tried to explain why some sections seem to violate the triadic form. J.N. Findlay, for instance—who, like Stace, associates dialectics “with the triad , or with triplicity ”—argues that stages can fit into that form in “more than one sense” (Findlay 1962: 66). The first sense of triplicity echoes the textbook, Being-Nothing-Becoming example. In a second sense, however, Findlay says, the dialectical moment or “contradictory breakdown” is not itself a separate stage, or “does not count as one of the stages”, but is a transition between opposed, “but complementary”, abstract stages that “are developed more or less concurrently” (Findlay 1962: 66). This second sort of triplicity could involve any number of stages: it “could readily have been expanded into a quadruplicity, a quintuplicity and so forth” (Findlay 1962: 66). Still, like Stace, he goes on to complain that many of the transitions in Hegel’s philosophy do not seem to fit the triadic pattern very well. In some triads, the second term is “the direct and obvious contrary of the first”—as in the case of Being and Nothing. In other cases, however, the opposition is, as Findlay puts it, “of a much less extreme character” (Findlay 1962: 69). In some triads, the third term obviously mediates between the first two terms. In other cases, however, he says, the third term is just one possible mediator or unity among other possible ones; and, in yet other cases, “the reconciling functions of the third member are not at all obvious” (Findlay 1962: 70).

Let us look more closely at one place where the “textbook example” of Being-Nothing-Becoming does not seem to describe the dialectical development of Hegel’s logic very well. In a later stage of the logic, the concept of Purpose goes through several iterations, from Abstract Purpose (EL §204), to Finite or Immediate Purpose (EL §205), and then through several stages of a syllogism (EL §206) to Realized Purpose (EL §210). Abstract Purpose is the thought of any kind of purposiveness, where the purpose has not been further determined or defined. It includes not just the kinds of purposes that occur in consciousness, such as needs or drives, but also the “internal purposiveness” or teleological view proposed by the ancient Greek philosopher, Aristotle (see entry on Aristotle ; EL Remark to §204), according to which things in the world have essences and aim to achieve (or have the purpose of living up to) their essences. Finite Purpose is the moment in which an Abstract Purpose begins to have a determination by fixing on some particular material or content through which it will be realized (EL §205). The Finite Purpose then goes through a process in which it, as the Universality, comes to realize itself as the Purpose over the particular material or content (and hence becomes Realized Purpose) by pushing out into Particularity, then into Singularity (the syllogism U-P-S), and ultimately into ‘out-thereness,’ or into individual objects out there in the world (EL §210; cf. Maybee 2009: 466–493).

Hegel’s description of the development of Purpose does not seem to fit the textbook Being-Nothing-Becoming example or the thesis-antithesis-synthesis model. According to the example and model, Abstract Purpose would be the moment of understanding or thesis, Finite Purpose would be the dialectical moment or antithesis, and Realized Purpose would be the speculative moment or synthesis. Although Finite Purpose has a different determination from Abstract Purpose (it refines the definition of Abstract Purpose), it is hard to see how it would qualify as strictly “opposed” to or as the “antithesis” of Abstract Purpose in the way that Nothing is opposed to or is the antithesis of Being.

There is an answer, however, to the criticism that many of the determinations are not “opposites” in a strict sense. The German term that is translated as “opposite” in Hegel’s description of the moments of dialectics (EL §§81, 82)— entgegensetzen —has three root words: setzen (“to posit or set”), gegen , (“against”), and the prefix ent -, which indicates that something has entered into a new state. The verb entgegensetzen can therefore literally be translated as “to set over against”. The “ engegengesetzte ” into which determinations pass, then, do not need to be the strict “opposites” of the first, but can be determinations that are merely “set against” or are different from the first ones. And the prefix ent -, which suggests that the first determinations are put into a new state, can be explained by Hegel’s claim that the finite determinations from the moment of understanding sublate (cancel but also preserve) themselves (EL §81): later determinations put earlier determinations into a new state by preserving them.

At the same time, there is a technical sense in which a later determination would still be the “opposite” of the earlier determination. Since the second determination is different from the first one, it is the logical negation of the first one, or is not -the-first-determination. If the first determination is “e”, for instance, because the new determination is different from that one, the new one is “not-e” (Kosek 1972: 240). Since Finite Purpose, for instance, has a definition or determination that is different from the definition that Abstract Purpose has, it is not -Abstract-Purpose, or is the negation or opposite of Abstract Purpose in that sense. There is therefore a technical, logical sense in which the second concept or form is the “opposite” or negation of—or is “not”—the first one—though, again, it need not be the “opposite” of the first one in a strict sense.

Other problems remain, however. Because the concept of Realized Purpose is defined through a syllogistic process, it is itself the product of several stages of development (at least four, by my count, if Realized Purpose counts as a separate determination), which would seem to violate a triadic model. Moreover, the concept of Realized Purpose does not, strictly speaking, seem to be the unity or combination of Abstract Purpose and Finite Purpose. Realized Purpose is the result of (and so unifies) the syllogistic process of Finite Purpose, through which Finite Purpose focuses on and is realized in a particular material or content. Realized Purpose thus seems to be a development of Finite Purpose, rather than a unity or combination of Abstract Purpose and Finite Purpose, in the way that Becoming can be said to be the unity or combination of Being and Nothing.

These sorts of considerations have led some scholars to interpret Hegel’s dialectics in a way that is implied by a more literal reading of his claim, in the Encyclopaedia Logic , that the three “sides” of the form of logic—namely, the moment of understanding, the dialectical moment, and the speculative moment—“are moments of each [or every; jedes ] logically-real , that is each [or every; jedes ] concept” (EL Remark to §79; this is an alternative translation). The quotation suggests that each concept goes through all three moments of the dialectical process—a suggestion reinforced by Hegel’s claim, in the Phenomenology , that the result of the process of determinate negation is that “a new form has thereby immediately arisen” (PhG-M §79). According to this interpretation, the three “sides” are not three different concepts or forms that are related to one another in a triad—as the textbook Being-Nothing-Becoming example suggests—but rather different momentary sides or “determinations” in the life, so to speak, of each concept or form as it transitions to the next one. The three moments thus involve only two concepts or forms: the one that comes first, and the one that comes next (examples of philosophers who interpret Hegel’s dialectics in this second way include Maybee 2009; Priest 1989: 402; Rosen 2014: 122, 132; and Winfield 1990: 56).

For the concept of Being, for example, its moment of understanding is its moment of stability, in which it is asserted to be pure presence. This determination is one-sided or restricted however, because, as we saw, it ignores another aspect of Being’s definition, namely, that Being has no content or determination, which is how Being is defined in its dialectical moment. Being thus sublates itself because the one-sidedness of its moment of understanding undermines that determination and leads to the definition it has in the dialectical moment. The speculative moment draws out the implications of these moments: it asserts that Being (as pure presence) implies nothing. It is also the “unity of the determinations in their comparison [ Entgegensetzung ]” (EL §82; alternative translation): since it captures a process from one to the other, it includes Being’s moment of understanding (as pure presence) and dialectical moment (as nothing or undetermined), but also compares those two determinations, or sets (- setzen ) them up against (- gegen ) each other. It even puts Being into a new state (as the prefix ent - suggests) because the next concept, Nothing, will sublate (cancel and preserve) Being.

The concept of Nothing also has all three moments. When it is asserted to be the speculative result of the concept of Being, it has its moment of understanding or stability: it is Nothing, defined as pure absence, as the absence of determination. But Nothing’s moment of understanding is also one-sided or restricted: like Being, Nothing is also an undefined content, which is its determination in its dialectical moment. Nothing thus sublates itself : since it is an undefined content , it is not pure absence after all, but has the same presence that Being did. It is present as an undefined content . Nothing thus sublates Being: it replaces (cancels) Being, but also preserves Being insofar as it has the same definition (as an undefined content) and presence that Being had. We can picture Being and Nothing like this (the circles have dashed outlines to indicate that, as concepts, they are each undefined; cf. Maybee 2009: 51):

In its speculative moment, then, Nothing implies presence or Being, which is the “unity of the determinations in their comparison [ Entgegensetzung ]” (EL §82; alternative translation), since it both includes but—as a process from one to the other—also compares the two earlier determinations of Nothing, first, as pure absence and, second, as just as much presence.

The dialectical process is driven to the next concept or form—Becoming—not by a triadic, thesis-antithesis-synthesis pattern, but by the one-sidedness of Nothing—which leads Nothing to sublate itself—and by the implications of the process so far. Since Being and Nothing have each been exhaustively analyzed as separate concepts, and since they are the only concepts in play, there is only one way for the dialectical process to move forward: whatever concept comes next will have to take account of both Being and Nothing at the same time. Moreover, the process revealed that an undefined content taken to be presence (i.e., Being) implies Nothing (or absence), and that an undefined content taken to be absence (i.e., Nothing) implies presence (i.e., Being). The next concept, then, takes Being and Nothing together and draws out those implications—namely, that Being implies Nothing, and that Nothing implies Being. It is therefore Becoming, defined as two separate processes: one in which Being becomes Nothing, and one in which Nothing becomes Being. We can picture Becoming this way (cf. Maybee 2009: 53):

In a similar way, a one-sidedness or restrictedness in the determination of Finite Purpose together with the implications of earlier stages leads to Realized Purpose. In its moment of understanding, Finite Purpose particularizes into (or presents) its content as “ something-presupposed ” or as a pre-given object (EL §205). I go to a restaurant for the purpose of having dinner, for instance, and order a salad. My purpose of having dinner particularizes as a pre-given object—the salad. But this object or particularity—e.g. the salad—is “inwardly reflected” (EL §205): it has its own content—developed in earlier stages—which the definition of Finite Purpose ignores. We can picture Finite Purpose this way:

In the dialectical moment, Finite Purpose is determined by the previously ignored content, or by that other content. The one-sidedness of Finite Purpose requires the dialectical process to continue through a series of syllogisms that determines Finite Purpose in relation to the ignored content. The first syllogism links the Finite Purpose to the first layer of content in the object: the Purpose or universality (e.g., dinner) goes through the particularity (e.g., the salad) to its content, the singularity (e.g., lettuce as a type of thing)—the syllogism U-P-S (EL §206). But the particularity (e.g., the salad) is itself a universality or purpose, “which at the same time is a syllogism within itself [ in sich ]” (EL Remark to §208; alternative translation), in relation to its own content. The salad is a universality/purpose that particularizes as lettuce (as a type of thing) and has its singularity in this lettuce here—a second syllogism, U-P-S. Thus, the first singularity (e.g., “lettuce” as a type of thing)—which, in this second syllogism, is the particularity or P —“ judges ” (EL §207) or asserts that “ U is S ”: it says that “lettuce” as a universality ( U ) or type of thing is a singularity ( S ), or is “this lettuce here”, for instance. This new singularity (e.g. “this lettuce here”) is itself a combination of subjectivity and objectivity (EL §207): it is an Inner or identifying concept (“lettuce”) that is in a mutually-defining relationship (the circular arrow) with an Outer or out-thereness (“this here”) as its content. In the speculative moment, Finite Purpose is determined by the whole process of development from the moment of understanding—when it is defined by particularizing into a pre-given object with a content that it ignores—to its dialectical moment—when it is also defined by the previously ignored content. We can picture the speculative moment of Finite Purpose this way:

Finite Purpose’s speculative moment leads to Realized Purpose. As soon as Finite Purpose presents all the content, there is a return process (a series of return arrows) that establishes each layer and redefines Finite Purpose as Realized Purpose. The presence of “this lettuce here” establishes the actuality of “lettuce” as a type of thing (an Actuality is a concept that captures a mutually-defining relationship between an Inner and an Outer [EL §142]), which establishes the “salad”, which establishes “dinner” as the Realized Purpose over the whole process. We can picture Realized Purpose this way:

If Hegel’s account of dialectics is a general description of the life of each concept or form, then any section can include as many or as few stages as the development requires. Instead of trying to squeeze the stages into a triadic form (cf. Solomon 1983: 22)—a technique Hegel himself rejects (PhG §50; cf. section 3 )—we can see the process as driven by each determination on its own account: what it succeeds in grasping (which allows it to be stable, for a moment of understanding), what it fails to grasp or capture (in its dialectical moment), and how it leads (in its speculative moment) to a new concept or form that tries to correct for the one-sidedness of the moment of understanding. This sort of process might reveal a kind of argument that, as Hegel had promised, might produce a comprehensive and exhaustive exploration of every concept, form or determination in each subject matter, as well as raise dialectics above a haphazard analysis of various philosophical views to the level of a genuine science.

We can begin to see why Hegel was motivated to use a dialectical method by examining the project he set for himself, particularly in relation to the work of David Hume and Immanuel Kant (see entries on Hume and Kant ). Hume had argued against what we can think of as the naïve view of how we come to have scientific knowledge. According to the naïve view, we gain knowledge of the world by using our senses to pull the world into our heads, so to speak. Although we may have to use careful observations and do experiments, our knowledge of the world is basically a mirror or copy of what the world is like. Hume argued, however, that naïve science’s claim that our knowledge corresponds to or copies what the world is like does not work. Take the scientific concept of cause, for instance. According to that concept of cause, to say that one event causes another is to say that there is a necessary connection between the first event (the cause) and the second event (the effect), such that, when the first event happens, the second event must also happen. According to naïve science, when we claim (or know) that some event causes some other event, our claim mirrors or copies what the world is like. It follows that the necessary, causal connection between the two events must itself be out there in the world. However, Hume argued, we never observe any such necessary causal connection in our experience of the world, nor can we infer that one exists based on our reasoning (see Hume’s A Treatise of Human Nature , Book I, Part III, Section II; Enquiry Concerning Human Understanding , Section VII, Part I). There is nothing in the world itself that our idea of cause mirrors or copies.

Kant thought Hume’s argument led to an unacceptable, skeptical conclusion, and he rejected Hume’s own solution to the skepticism (see Kant’s Critique of Pure Reason , B5, B19–20). Hume suggested that our idea of causal necessity is grounded merely in custom or habit, since it is generated by our own imaginations after repeated observations of one sort of event following another sort of event (see Hume’s A Treatise of Human Nature , Book I, Section VI; Hegel also rejected Hume’s solution, see EL §39). For Kant, science and knowledge should be grounded in reason, and he proposed a solution that aimed to reestablish the connection between reason and knowledge that was broken by Hume’s skeptical argument. Kant’s solution involved proposing a Copernican revolution in philosophy ( Critique of Pure Reason , Bxvi). Nicholas Copernicus was the Polish astronomer who said that the earth revolves around the sun, rather than the other way around. Kant proposed a similar solution to Hume’s skepticism. Naïve science assumes that our knowledge revolves around what the world is like, but, Hume’s criticism argued, this view entails that we cannot then have knowledge of scientific causes through reason. We can reestablish a connection between reason and knowledge, however, Kant suggested, if we say—not that knowledge revolves around what the world is like—but that knowledge revolves around what we are like . For the purposes of our knowledge, Kant said, we do not revolve around the world—the world revolves around us. Because we are rational creatures, we share a cognitive structure with one another that regularizes our experiences of the world. This intersubjectively shared structure of rationality—and not the world itself—grounds our knowledge.

However, Kant’s solution to Hume’s skepticism led to a skeptical conclusion of its own that Hegel rejected. While the intersubjectively shared structure of our reason might allow us to have knowledge of the world from our perspective, so to speak, we cannot get outside of our mental, rational structures to see what the world might be like in itself. As Kant had to admit, according to his theory, there is still a world in itself or “Thing-in-itself” ( Ding an sich ) about which we can know nothing (see, e.g., Critique of Pure Reason , Bxxv–xxvi). Hegel rejected Kant’s skeptical conclusion that we can know nothing about the world- or Thing-in-itself, and he intended his own philosophy to be a response to this view (see, e.g., EL §44 and the Remark to §44).

How did Hegel respond to Kant’s skepticism—especially since Hegel accepted Kant’s Copernican revolution, or Kant’s claim that we have knowledge of the world because of what we are like, because of our reason? How, for Hegel, can we get out of our heads to see the world as it is in itself? Hegel’s answer is very close to the ancient Greek philosopher Aristotle’s response to Plato. Plato argued that we have knowledge of the world only through the Forms. The Forms are perfectly universal, rational concepts or ideas. Because the world is imperfect, however, Plato exiled the Forms to their own realm. Although things in the world get their definitions by participating in the Forms, those things are, at best, imperfect copies of the universal Forms (see, e.g., Parmenides 131–135a). The Forms are therefore not in this world, but in a separate realm of their own. Aristotle argued, however, that the world is knowable not because things in the world are imperfect copies of the Forms, but because the Forms are in things themselves as the defining essences of those things (see, e.g., De Anima [ On the Soul ], Book I, Chapter 1 [403a26–403b18]; Metaphysics , Book VII, Chapter 6 [1031b6–1032a5] and Chapter 8 [1033b20–1034a8]).

In a similar way, Hegel’s answer to Kant is that we can get out of our heads to see what the world is like in itself—and hence can have knowledge of the world in itself—because the very same rationality or reason that is in our heads is in the world itself . As Hegel apparently put it in a lecture, the opposition or antithesis between the subjective and objective disappears by saying, as the Ancients did,

that nous governs the world, or by our own saying that there is reason in the world, by which we mean that reason is the soul of the world, inhabits it, and is immanent in it, as it own, innermost nature, its universal. (EL-GSH Addition 1 to §24)

Hegel used an example familiar from Aristotle’s work to illustrate this view:

“to be an animal”, the kind considered as the universal, pertains to the determinate animal and constitutes its determinate essentiality. If we were to deprive a dog of its animality we could not say what it is. (EL-GSH Addition 1 to §24; cf. SL-dG 16–17, SL-M 36-37)

Kant’s mistake, then, was that he regarded reason or rationality as only in our heads, Hegel suggests (EL §§43–44), rather than in both us and the world itself (see also below in this section and section 4 ). We can use our reason to have knowledge of the world because the very same reason that is in us, is in the world itself as it own defining principle. The rationality or reason in the world makes reality understandable, and that is why we can have knowledge of, or can understand, reality with our rationality. Dialectics—which is Hegel’s account of reason—characterizes not only logic, but also “everything true in general” (EL Remark to §79).

But why does Hegel come to define reason in terms of dialectics, and hence adopt a dialectical method? We can begin to see what drove Hegel to adopt a dialectical method by returning once again to Plato’s philosophy. Plato argued that we can have knowledge of the world only by grasping the Forms, which are perfectly universal, rational concepts or ideas. Because things in the world are so imperfect, however, Plato concluded that the Forms are not in this world, but in a realm of their own. After all, if a human being were perfectly beautiful, for instance, then he or she would never become not-beautiful. But human beings change, get old, and die, and so can be, at best, imperfect copies of the Form of beauty—though they get whatever beauty they have by participating in that Form. Moreover, for Plato, things in the world are such imperfect copies that we cannot gain knowledge of the Forms by studying things in the world, but only through reason, that is, only by using our rationality to access the separate realm of the Forms (as Plato argued in the well-known parable of the cave; Republic , Book 7, 514–516b).

Notice, however, that Plato’s conclusion that the Forms cannot be in this world and so must be exiled to a separate realm rests on two claims. First, it rests on the claim that the world is an imperfect and messy place—a claim that is hard to deny. But it also rests on the assumption that the Forms—the universal, rational concepts or ideas of reason itself—are static and fixed, and so cannot grasp the messiness within the imperfect world. Hegel is able to link reason back to our messy world by changing the definition of reason. Instead of saying that reason consists of static universals, concepts or ideas, Hegel says that the universal concepts or forms are themselves messy . Against Plato, Hegel’s dialectical method allows him to argue that universal concepts can “overgrasp” (from the German verb übergreifen ) the messy, dialectical nature of the world because they, themselves, are dialectical . Moreover, because later concepts build on or sublate (cancel, but also preserve) earlier concepts, the later, more universal concepts grasp the dialectical processes of earlier concepts. As a result, higher-level concepts can grasp not only the dialectical nature of earlier concepts or forms, but also the dialectical processes that make the world itself a messy place. The highest definition of the concept of beauty, for instance, would not take beauty to be fixed and static, but would include within it the dialectical nature or finiteness of beauty, the idea that beauty becomes, on its own account, not-beauty. This dialectical understanding of the concept of beauty can then overgrasp the dialectical and finite nature of beauty in the world, and hence the truth that, in the world, beautiful things themselves become not-beautiful, or might be beautiful in one respect and not another. Similarly, the highest determination of the concept of “tree” will include within its definition the dialectical process of development and change from seed to sapling to tree. As Hegel says, dialectics is “the principle of all natural and spiritual life” (SL-M 56; SL-dG 35), or “the moving soul of scientific progression” (EL §81). Dialectics is what drives the development of both reason as well as of things in the world. A dialectical reason can overgrasp a dialectical world.

Two further journeys into the history of philosophy will help to show why Hegel chose dialectics as his method of argument. As we saw, Hegel argues against Kant’s skepticism by suggesting that reason is not only in our heads, but in the world itself. To show that reason is in the world itself, however, Hegel has to show that reason can be what it is without us human beings to help it. He has to show that reason can develop on its own, and does not need us to do the developing for it (at least for those things in the world that are not human-created). As we saw (cf. section 1 ), central to Hegel’s dialectics is the idea that concepts or forms develop on their own because they “self-sublate”, or sublate (cancel and preserve) themselves , and so pass into subsequent concepts or forms on their own accounts, because of their own, dialectical natures. Thus reason, as it were, drives itself, and hence does not need our heads to develop it. Hegel needs an account of self-driving reason to get beyond Kant’s skepticism.

Ironically, Hegel derives the basic outlines of his account of self-driving reason from Kant. Kant divided human rationality into two faculties: the faculty of the understanding and the faculty of reason. The understanding uses concepts to organize and regularize our experiences of the world. Reason’s job is to coordinate the concepts and categories of the understanding by developing a completely unified, conceptual system, and it does this work, Kant thought, on its own, independently of how those concepts might apply to the world. Reason coordinates the concepts of the understanding by following out necessary chains of syllogisms to produce concepts that achieve higher and higher levels of conceptual unity. Indeed, this process will lead reason to produce its own transcendental ideas, or concepts that go beyond the world of experience. Kant calls this necessary, concept-creating reason “speculative” reason (cf. Critique of Pure Reason , Bxx–xxi, A327/B384). Reason creates its own concepts or ideas—it “speculates”—by generating new and increasingly comprehensive concepts of its own, independently of the understanding. In the end, Kant thought, reason will follow out such chains of syllogisms until it develops completely comprehensive or unconditioned universals—universals that contain all of the conditions or all of the less-comprehensive concepts that help to define them. As we saw (cf. section 1 ), Hegel’s dialectics adopts Kant’s notion of a self-driving and concept-creating “speculative” reason, as well as Kant’s idea that reason aims toward unconditioned universality or absolute concepts.

Ultimately, Kant thought, reasons’ necessary, self-driving activity will lead it to produce contradictions—what he called the “antinomies”, which consist of a thesis and antithesis. Once reason has generated the unconditioned concept of the whole world, for instance, Kant argued, it can look at the world in two, contradictory ways. In the first antinomy, reason can see the world (1) as the whole totality or as the unconditioned, or (2) as the series of syllogisms that led up to that totality. If reason sees the world as the unconditioned or as a complete whole that is not conditioned by anything else, then it will see the world as having a beginning and end in terms of space and time, and so will conclude (the thesis) that the world has a beginning and end or limit. But if reason sees the world as the series, in which each member of the series is conditioned by the previous member, then the world will appear to be without a beginning and infinite, and reason will conclude (the antithesis) that the world does not have a limit in terms of space and time (cf. Critique of Pure Reason , A417–18/B445–6). Reason thus leads to a contradiction: it holds both that the world has a limit and that it does not have a limit at the same time. Because reason’s own process of self-development will lead it to develop contradictions or to be dialectical in this way, Kant thought that reason must be kept in check by the understanding. Any conclusions that reason draws that do not fall within the purview of the understanding cannot be applied to the world of experience, Kant said, and so cannot be considered genuine knowledge ( Critique of Pure Reason , A506/B534).

Hegel adopts Kant’s dialectical conception of reason, but he liberates reason for knowledge from the tyranny of the understanding. Kant was right that reason speculatively generates concepts on its own, and that this speculative process is driven by necessity and leads to concepts of increasing universality or comprehensiveness. Kant was even right to suggest—as he had shown in the discussion of the antinomies—that reason is dialectical, or necessarily produces contradictions on its own. Again, Kant’s mistake was that he fell short of saying that these contradictions are in the world itself. He failed to apply the insights of his discussion of the antinomies to “ things in themselves ” (SL-M 56; SL-dG 35; see also section 4 ). Indeed, Kant’s own argument proves that the dialectical nature of reason can be applied to things themselves. The fact that reason develops those contradictions on its own, without our heads to help it , shows that those contradictions are not just in our heads, but are objective, or in the world itself. Kant, however, failed to draw this conclusion, and continued to regard reason’s conclusions as illusions. Still, Kant’s philosophy vindicated the general idea that the contradictions he took to be illusions are both objective—or out there in the world—and necessary. As Hegel puts it, Kant vindicates the general idea of “the objectivity of the illusion and the necessity of the contradiction which belongs to the nature of thought determinations” (SL-M 56; cf. SL-dG 35), or to the nature of concepts themselves.

The work of Johann Gottlieb Fichte (see entry on Fichte ) showed Hegel how dialectics can get beyond Kant—beyond the contradictions that, as Kant had shown, reason (necessarily) develops on its own, beyond the reductio ad absurdum argument (which, as we saw above, holds that a contradiction leads to nothingness), and beyond Kant’s skepticism, or Kant’s claim that reason’s contradictions must be reined in by the understanding and cannot count as knowledge. Fichte argued that the task of discovering the foundation of all human knowledge leads to a contradiction or opposition between the self and the not-self (it is not important, for our purposes, why Fichte held this view). The kind of reasoning that leads to this contradiction, Fichte said, is the analytical or antithetical method of reasoning, which involves drawing out an opposition between elements (in this case, the self and not-self) that are being compared to, or equated with, one another. While the traditional reductio ad absurdum argument would lead us to reject both sides of the contradiction and start from scratch, Fichte argued that the contradiction or opposition between the self and not-self can be resolved. In particular, the contradiction is resolved by positing a third concept—the concept of divisibility—which unites the two sides ( The Science of Knowledge , I: 110–11; Fichte 1982: 108–110). The concept of divisibility is produced by a synthetic procedure of reasoning, which involves “discovering in opposites the respect in which they are alike ” ( The Science of Knowledge , I: 112–13; Fichte 1982: 111). Indeed, Fichte argued, not only is the move to resolve contradictions with synthetic concepts or judgments possible, it is necessary . As he says of the move from the contradiction between self and not-self to the synthetic concept of divisibility,

there can be no further question as to the possibility of this [synthesis], nor can any ground for it be given; it is absolutely possible, and we are entitled to it without further grounds of any kind. ( The Science of Knowledge , I: 114; Fichte 1982: 112)

Since the analytical method leads to oppositions or contradictions, he argued, if we use only analytic judgments, “we not only do not get very far, as Kant says; we do not get anywhere at all” ( The Science of Knowledge , I: 113; Fichte 1982: 112). Without the synthetic concepts or judgments, we are left, as the classic reductio ad absurdum argument suggests, with nothing at all. The synthetic concepts or judgments are thus necessary to get beyond contradiction without leaving us with nothing.

Fichte’s account of the synthetic method provides Hegel with the key to moving beyond Kant. Fichte suggested that a synthetic concept that unifies the results of a dialectically-generated contradiction does not completely cancel the contradictory sides, but only limits them. As he said, in general, “[t]o limit something is to abolish its reality, not wholly , but in part only” ( The Science of Knowledge , I: 108; Fichte 1982: 108). Instead of concluding, as a reductio ad absurdum requires, that the two sides of a contradiction must be dismissed altogether, the synthetic concept or judgment retroactively justifies the opposing sides by demonstrating their limit, by showing which part of reality they attach to and which they do not ( The Science of Knowledge , I: 108–10; Fichte 1982: 108–9), or by determining in what respect and to what degree they are each true. For Hegel, as we saw (cf. section 1 ), later concepts and forms sublate—both cancel and preserve —earlier concepts and forms in the sense that they include earlier concepts and forms in their own definitions. From the point of view of the later concepts or forms, the earlier ones still have some validity, that is, they have a limited validity or truth defined by the higher-level concept or form.

Dialectically generated contradictions are therefore not a defect to be reigned in by the understanding, as Kant had said, but invitations for reason to “speculate”, that is, for reason to generate precisely the sort of increasingly comprehensive and universal concepts and forms that Kant had said reason aims to develop. Ultimately, Hegel thought, as we saw (cf. section 1 ), the dialectical process leads to a completely unconditioned concept or form for each subject matter—the Absolute Idea (logic), Absolute Spirit (phenomenology), Absolute Idea of right and law ( Philosophy of Right ), and so on—which, taken together, form the “circle of circles” (EL §15) that constitutes the whole philosophical system or “Idea” (EL §15) that both overgrasps the world and makes it understandable (for us).

Note that, while Hegel was clearly influenced by Fichte’s work, he never adopted Fichte’s triadic “thesis—antithesis—synthesis” language in his descriptions of his own philosophy (Mueller 1958: 411–2; Solomon 1983: 23), though he did apparently use it in his lectures to describe Kant’s philosophy (LHP III: 477). Indeed, Hegel criticized formalistic uses of the method of “ triplicity [Triplizität]” (PhG-P §50) inspired by Kant—a criticism that could well have been aimed at Fichte. Hegel argued that Kantian-inspired uses of triadic form had been reduced to “a lifeless schema” and “an actual semblance [ eigentlichen Scheinen ]” (PhG §50; alternative translation) that, like a formula in mathematics, was simply imposed on top of subject matters. Instead, a properly scientific use of Kant’s “triplicity” should flow—as he said his own dialectical method did (see section 1 )—out of “the inner life and self-movement” (PhG §51) of the content.

Scholars have often questioned whether Hegel’s dialectical method is logical. Some of their skepticism grows out of the role that contradiction plays in his thought and argument. While many of the oppositions embedded in the dialectical development and the definitions of concepts or forms are not contradictions in the strict sense, as we saw ( section 2 , above), scholars such as Graham Priest have suggested that some of them arguably are (Priest 1989: 391). Hegel even holds, against Kant (cf. section 3 above), that there are contradictions, not only in thought, but also in the world. Motion, for instance, Hegel says, is an “ existent contradiction”. As he describes it:

Something moves, not because now it is here and there at another now, but because in one and the same now it is here and not here, because in this here, it is and is not at the same time. (SL-dG 382; cf. SL-M 440)

Kant’s sorts of antinomies (cf. section 3 above) or contradictions more generally are therefore, as Hegel puts it in one place, “in all objects of all kinds, in all representations, concepts and ideas” (EL-GSH Remark to §48). Hegel thus seems to reject, as he himself explicitly claims (SL-M 439–40; SL-dG 381–82), the law of non-contradiction, which is a fundamental principle of formal logic—the classical, Aristotelian logic (see entries on Aristotle’s Logic and Contradiction ) that dominated during Hegel’s lifetime as well as the dominant systems of symbolic logic today (cf. Priest 1989: 391; Düsing 2010: 97–103). According to the law of non-contradiction, something cannot be both true and false at the same time or, put another way, “x” and “not-x” cannot both be true at the same time.

Hegel’s apparent rejection of the law of non-contradiction has led some interpreters to regard his dialectics as illogical, even “absurd” (Popper 1940: 420; 1962: 330; 2002: 443). Karl R. Popper, for instance, argued that accepting Hegel’s and other dialecticians’ rejection of the law of non-contradiction as part of both a logical theory and a general theory of the world “would mean a complete breakdown of science” (Popper 1940: 408; 1962: 317; 2002: 426). Since, according to today’s systems of symbolic logic, he suggested, the truth of a contradiction leads logically to any claim (any claim can logically be inferred from two contradictory claims), if we allow contradictory claims to be valid or true together, then we would have no reason to rule out any claim whatsoever (Popper 1940: 408–410; 1962: 317–319; 2002: 426–429).

Popper was notoriously hostile toward Hegel’s work (cf. Popper 2013: 242–289; for a scathing criticism of Popper’s analysis see Kaufmann 1976 [1972]), but, as Priest has noted (Priest 1989: 389–91), even some sympathetic interpreters have been inspired by today’s dominant systems of symbolic logic to hold that the kind of contradiction that is embedded in Hegel’s dialectics cannot be genuine contradiction in the strict sense. While Dieter Wandschneider, for instance, grants that his sympathetic theory of dialectic “is not presented as a faithful interpretation of the Hegelian text” (Wandschneider 2010: 32), he uses the same logical argument that Popper offered in defense of the claim that “dialectical contradiction is not a ‘normal’ contradiction, but one that is actually only an apparent contradiction” (Wandschneider 2010: 37). The suggestion (by the traditional, triadic account of Hegel’s dialectics, cf. section 2 , above) that Being and Nothing (or non-being) is a contradiction, for instance, he says, rests on an ambiguity. Being is an undefined content, taken to mean being or presence, while Nothing is an undefined content, taken to mean nothing or absence ( section 2 , above; cf. Wandschneider 2010: 34–35). Being is Nothing (or non-being) with respect to the property they have as concepts, namely, that they both have an undefined content. But Being is not Nothing (or non-being) with respect to their meaning (Wandschneider 2010: 34–38). The supposed contradiction between them, then, Wandschneider suggests, takes place “in different respects ”. It is therefore only an apparent contradiction. “Rightly understood”, he concludes, “there can be no talk of contradiction ” (Wandschneider 2010: 38).

Inoue Kazumi also argues that dialectical contradiction in the Hegelian sense does not violate the law of non-contradiction (Inoue 2014: 121–123), and he rejects Popper’s claim that Hegel’s dialectical method is incompatible with good science. A dialectical contradiction, Inoue says, is a contradiction that arises when the same topic is considered from different vantage points, but each vantage point by itself does not violate the law of non-contradiction (Inoue 2014: 120). The understanding leads to contradictions, as Hegel said (cf. section 3 above), because it examines a topic from a fixed point of view; reason embraces contradictions because it examines a topic from multiple points of view (Inoue 2014: 121). The geocentric theory that the sun revolves around the Earth and the heliocentric theory that the Earth revolves around the sun, for instance, Inoue suggests, are both correct from certain points of view. We live our everyday lives from a vantage point in which the sun makes a periodic rotation around the Earth roughly every 24 hours. Astronomers make their observations from a geocentric point of view and then translate those observations into a heliocentric one. From these points of view, the geocentric account is not incorrect. But physics, particularly in its concepts of mass and force, requires the heliocentric account. For science—which takes all these points of view into consideration—both theories are valid: they are dialectically contradictory, though neither theory, by itself, violates the law of non-contradiction (Inoue 2014: 126–127). To insist that the Earth really revolves around the sun is merely an irrational, reductive prejudice, theoretically and practically (Inoue 2014: 126). Dialectical contradictions, Inoue says, are, as Hegel said, constructive: they lead to concepts or points of view that grasp the world from ever wider and more encompassing perspectives, culminating ultimately in the “Absolute” (Inoue 2014: 121; cf. section 1 , above). Hegel’s claim that motion violates the law of non-contradiction, Inoue suggests, is an expression of the idea that contradictory claims can be true when motion is described from more than one point of view (Inoue 2014: 123). (For a similar reading of Hegel’s conception of dialectical contradiction, which influenced Inoue’s account [Inoue 2014: 121], see Düsing 2010: 102–103.)

Other interpreters, however, have been inspired by Hegel’s dialectics to develop alternative systems of logic that do not subscribe to the law of non-contradiction. Priest, for instance, has defended Hegel’s rejection of the law of non-contradiction (cf. Priest 1989; 1997 [2006: 4]). The acceptance of some contradictions, he has suggested, does not require the acceptance of all contradictions (Priest 1989: 392). Popper’s logical argument is also unconvincing. Contradictions lead logically to any claim whatsoever, as Popper said, only if we presuppose that nothing can be both true and false at the same time (i.e. only if we presuppose that the law of non-contradiction is correct), which is just what Hegel denies. Popper’s logical argument thus assumes what it is supposed to prove or begs the question (Priest 1989: 392; 1997 [2006: 5–6]), and so is not convincing. Moreover, consistency (not allowing contradictions), Priest suggests, is actually “a very weak constraint” (Priest 1997 [2006: 104]) on what counts as a rational inference. Other principles or criteria—such as being strongly disproved (or supported) by the data—are more important for determining whether a claim or inference is rational (Priest 1997 [2006: 105]). And, as Hegel pointed out, Priest says, the data—namely, “the world as it appears ” (as Hegel puts it in EL) or “ordinary experience itself” (as Hegel puts it in SL)—suggest that there are indeed contradictions (EL Remark to §48; SL-dG 382; cf. SL-M 440; Priest 1989: 389, 399–400). Hegel is right, for instance, Priest argues, that change, and motion in particular, are examples of real or existing contradictions (Priest 1985; 1989: 396–97; 1997 [2006: 172–181, 213–15]). What distinguishes motion, as a process, from a situation in which something is simply here at one time and then some other place at some other time is the embodiment of contradiction: that, in a process of motion, there is one (span of) time in which something is both here and not here at the same time (in that span of time) (Priest 1985: 340–341; 1997 [2006: 172–175, 213–214]). A system of logic, Priest suggests, is always just a theory about what good reasoning should be like (Priest 1989: 392). A dialectical logic that admits that there are “dialetheia” or true contradictions (Priest 1989: 388), he says, is a broader theory or version of logic than traditional, formal logics that subscribe to the law of non-contradiction. Those traditional logics apply only to topics or domains that are consistent, primarily domains that are “static and changeless” (Priest 1989: 391; cf. 395); dialectical/dialetheic logic handles consistent domains, but also applies to domains in which there are dialetheia. Thus Priest, extending Hegel’s own concept of aufheben (“to sublate”; cf. section 1 , above), suggests that traditional “formal logic is perfectly valid in its domain, but dialectical (dialetheic) logic is more general” (Priest 1989: 395). (For an earlier example of a logical system that allows contradiction and was inspired in part by Hegel [and Marx], see Jaśkowski 1999: 36 [1969: 143] [cf. Inoue 2014: 128–129]. For more on dialetheic logic generally, see the entry on Dialetheism .)

Worries that Hegel’s arguments fail to fit his account of dialectics (see section 2 , above) have led some interpreters to conclude that his method is arbitrary or that his works have no single dialectical method at all (Findlay 1962: 93; Solomon 1983: 21). These interpreters reject the idea that there is any logical necessity to the moves from stage to stage. “[T]he important point to make here, and again and again”, Robert C. Solomon writes, for instance,

is that the transition from the first form to the second, or the transition from the first form of the Phenomenology all the way to the last, is not in any way a deductive necessity. The connections are anything but entailments, and the Phenomenology could always take another route and other starting points. (Solomon 1983: 230)

In a footnote to this passage, Solomon adds “that a formalization of Hegel’s logic, however ingenious, is impossible” (Solomon 1983: 230).

Some scholars have argued that Hegel’s necessity is not intended to be logical necessity. Walter Kaufmann suggested, for instance, that the necessity at work in Hegel’s dialectic is a kind of organic necessity. The moves in the Phenomenology , he said, follow one another “in the way in which, to use a Hegelian image from the preface, bud, blossom and fruit succeed each other” (Kaufmann 1965: 148; 1966: 132). Findlay argued that later stages provide what he called a “ higher-order comment ” on earlier stages, even if later stages do not follow from earlier ones in a trivial way (Findlay 1966: 367). Solomon suggested that the necessity that Hegel wants is not “‘necessity’ in the modern sense of ‘logical necessity,’” (Solomon 1983: 209), but a kind of progression (Solomon 1983: 207), or a “necessity within a context for some purpose ” (Solomon 1983: 209). John Burbidge defines Hegel’s necessity in terms of three senses of the relationship between actuality and possibility, only the last of which is logical necessity (Burbidge 1981: 195–6).

Other scholars have defined the necessity of Hegel’s dialectics in terms of a transcendental argument. A transcendental argument begins with uncontroversial facts of experience and tries to show that other conditions must be present—or are necessary—for those facts to be possible. Jon Stewart argues, for instance, that “Hegel’s dialectic in the Phenomenology is a transcendental account” in this sense, and thus has the necessity of that form of argument (Stewart 2000: 23; cf. Taylor 1975: 97, 226–7; for a critique of this view, see Pinkard 1988: 7, 15).

Some scholars have avoided these debates by interpreting Hegel’s dialectics in a literary way. In his examination of the epistemological theory of the Phenomenology , for instance, Kenneth R. Westphal offers “a literary model” of Hegel’s dialectics based on the story of Sophocles’ play Antigone (Westphal 2003: 14, 16). Ermanno Bencivenga offers an interpretation that combines a narrative approach with a concept of necessity. For him, the necessity of Hegel’s dialectical logic can be captured by the notion of telling a good story—where “good” implies that the story is both creative and correct at the same time (Bencivenga 2000: 43–65).

Debate over whether Hegel’s dialectical logic is logical may also be fueled in part by discomfort with his particular brand of logic. Unlike today’s symbolic logics, Hegel’s logic is not only syntactic, but also semantic (cf. Berto 2007; Maybee 2009: xx–xxv; Margolis 2010: 193–94). Hegel’s interest in semantics appears, for instance, in the very first stages of his logic, where the difference between Being and Nothing is “something merely meant ” (EL-GSH Remark to §87; cf. section 2 above). While some of the moves from stage to stage are driven by syntactic necessity, other moves are driven by the meanings of the concepts in play. Indeed, Hegel rejected what he regarded as the overly formalistic logics that dominated the field during his day (EL Remark to §162; SL-M 43–44; SL-dG 24). A logic that deals only with the forms of logical arguments and not the meanings of the concepts used in those argument forms will do no better in terms of preserving truth than the old joke about computer programs suggests: garbage in, garbage out. In those logics, if we (using today’s versions of formal, symbolic logic) plug in something for the P or Q (in the proposition “if P then Q ” or “ P → Q ”, for instance) or for the “ F ”, “ G ”, or “ x ” (in the proposition “if F is x , then G is x ” or “ F x → G x ”, for instance) that means something true, then the syntax of formal logics will preserve that truth. But if we plug in something for those terms that is untrue or meaningless (garbage in), then the syntax of formal logic will lead to an untrue or meaningless conclusion (garbage out). Today’s versions of prepositional logic also assume that we know what the meaning of “is” is. Against these sorts of logics, Hegel wanted to develop a logic that not only preserved truth, but also determined how to construct truthful claims in the first place. A logic that defines concepts (semantics) as well as their relationships with one another (syntax) will show, Hegel thought, how concepts can be combined into meaningful forms. Because interpreters are familiar with modern logics focused on syntax, however, they may regard Hegel’s syntactic and semantic logic as not really logical (cf. Maybee 2009: xvii–xxv).

In Hegel’s other works, the moves from stage to stage are often driven, not only by syntax and semantics—that is, by logic (given his account of logic)—but also by considerations that grow out of the relevant subject matter. In the Phenomenology , for instance, the moves are driven by syntax, semantics, and by phenomenological factors. Sometimes a move from one stage to the next is driven by a syntactic need—the need to stop an endless, back-and-forth process, for instance, or to take a new path after all the current options have been exhausted (cf. section 5 ). Sometimes, a move is driven by the meaning of a concept, such as the concept of a “This” or “Thing”. And sometimes a move is driven by a phenomenological need or necessity—by requirements of consciousness , or by the fact that the Phenomenology is about a consciousness that claims to be aware of (or to know) something. The logic of the Phenomenology is thus a phenomeno -logic, or a logic driven by logic—syntax and semantics—and by phenomenological considerations. Still, interpreters such as Quentin Lauer have suggested that, for Hegel,

phenomeno-logy is a logic of appearing, a logic of implication, like any other logic, even though not of the formal entailment with which logicians and mathematicians are familiar. (Lauer 1976: 3)

Lauer warns us against dismissing the idea that there is any implication or necessity in Hegel’s method at all (Lauer 1976: 3). (Other scholars who also believe there is a logical necessity to the dialectics of the Phenomenology include Hyppolite 1974: 78–9 and H.S. Harris 1997: xii.)

We should also be careful not to exaggerate the “necessity” of formal, symbolic logics. Even in these logics, there can often be more than one path from some premises to the same conclusion, logical operators can be dealt with in different orders, and different sets of operations can be used to reach the same conclusions. There is therefore often no strict, necessary “entailment” from one step to the next, even though the conclusion might be entailed by the whole series of steps, taken together. As in today’s logics, then, whether Hegel’s dialectics counts as logical depends on the degree to which he shows that we are forced—necessarily—from earlier stages or series of stages to later stages (see also section 5 ).

Although Hegel’s dialectics is driven by syntax, semantics and considerations specific to the different subject matters ( section 4 above), several important syntactic patterns appear repeatedly throughout his works. In many places, the dialectical process is driven by a syntactic necessity that is really a kind of exhaustion: when the current strategy has been exhausted, the process is forced, necessarily, to employ a new strategy. As we saw ( section 2 ), once the strategy of treating Being and Nothing as separate concepts is exhausted, the dialectical process must, necessarily, adopt a different strategy, namely, one that takes the two concepts together. The concept of Becoming captures the first way in which Being and Nothing are taken together. In the stages of Quantum through Number, the concepts of One and Many take turns defining the whole quantity as well as the quantitative bits inside that make it up: first, the One is the whole, while the Many are the bits; then the whole and the bits are all Ones; then the Many is the whole, while the bits are each a One; and finally the whole and the bits are all a Many. We can picture the development like this (cf. Maybee 2009, xviii–xix):

Since One and Many have been exhausted, the next stage, Ratio, must, necessarily, employ a different strategy to grasp the elements in play. Just as Being-for-itself is a concept of universality for Quality and captures the character of a set of something-others in its content (see section 1 ), so Ratio (the whole rectangle with rounded corners) is a concept of universality for Quantity and captures the character of a set of quantities in its content (EL §105–6; cf. Maybee 2009, xviii–xix, 95–7). In another version of syntactic necessity driven by exhaustion, the dialectical development will take account of every aspect or layer, so to speak, of a concept or form—as we saw in the stages of Purpose outlined above, for instance ( section 2 ). Once all the aspects or layers of a concept or form have been taken account of and so exhausted, the dialectical development must also, necessarily, employ a different strategy in the next stage to grasp the elements in play.

In a second, common syntactic pattern, the dialectical development leads to an endless, back-and-forth process—a “bad” (EL-BD §94) or “spurious” (EL-GSH §94) infinity—between two concepts or forms. Hegel’s dialectics cannot rest with spurious infinities. So long as the dialectical process is passing endlessly back and forth between two elements, it is never finished, and the concept or form in play cannot be determined. Spurious infinities must therefore be resolved or stopped, and they are always resolved by a higher-level, more universal concept. In some cases, a new, higher-level concept is introduced that stops the spurious infinity by grasping the whole, back-and-forth process. Being-for-itself (cf. section 1 ), for instance, is introduced as a new, more universal concept that embraces—and hence stops—the whole, back-and-forth process between “something-others”. However, if the back-and-forth process takes place between a concept and its own content—in which case the concept already embraces the content—then that embracing concept is redefined in a new way that grasps the whole, back-and-forth process. The new definition raises the embracing concept to a higher level of universality—as a totality (an “all”) or as a complete and completed concept. Examples from logic include the redefinition of Appearance as the whole World of Appearance (EL §132; cf. SL-M 505–7, SL-dG 443–4), the move in which the endless, back-and-forth process of Real Possibility redefines the Condition as a totality (EL §147; cf. SL-M 547, SL-dG 483), and the move in which a back-and-forth process created by finite Cognition and finite Willing redefines the Subjective Idea as Absolute Idea (EL §§234–5; cf. SL-M 822–3, SL-dG 733–4).

Some of the most famous terms in Hegel’s works—“in itself [ an sich ]”, “for itself [ für sich ]” and “in and for itself [ an und für sich ]”—capture other, common, syntactic patterns. A concept or form is “in itself” when it has a determination that it gets by being defined against its “other” (cf. Being-in-itself, EL §91). A concept or form is “for itself” when it is defined only in relation to its own content, so that, while it is technically defined in relation to an “other”, the “other” is not really an “other” for it. As a result, it is really defined only in relation to itself. Unlike an “in itself” concept or form, then, a “for itself” concept or form seems to have its definition on its own, or does not need a genuine “other” to be defined (like other concepts or forms, however, “for itself” concepts or forms turn out to be dialectical too, and hence push on to new concepts or forms). In the logic, Being-for-itself (cf. section 1 ), which is defined by embracing the “something others” in its content, is the first, “for itself” concept or form.

A concept or form is “in and for itself” when it is doubly “for itself”, or “for itself” not only in terms of content —insofar as it embraces its content—but also in terms of form or presentation, insofar as it also has the activity of presenting its content. It is “for itself” (embraces its content) for itself (through its own activity), or not only embraces its content (the “for itself” of content) but also presents its content through its own activity (the “for itself” of form). The second “for itself” of form provides the concept with a logical activity (i.e., presenting its content) and hence a definition that goes beyond—and so is separate from—the definition that its content has. Since it has a definition of its own that is separate from the definition of its content, it comes to be defined—in the “in itself” sense— against its content, which has become its “other”. Because this “other” is still its own content, however, the concept or form is both “in itself” but also still “for itself” at the same time, or is “in and for itself” (EL §§148–9; cf. Maybee 2009: 244–6). The “in and for itself” relationship is the hallmark of a genuine Concept (EL §160), and captures the idea that a genuine concept is defined not only from the bottom up by its content, but also from the top down through its own activity of presenting its content. The genuine concept of animal, for instance, is not only defined by embracing its content (namely, all animals) from the bottom up, but also has a definition of its own, separate from that content, that leads it to determine (and so present), from the top down, what counts as an animal.

Other technical, syntactic terms include aufheben (“to sublate”), which we already saw ( section 1 ), and “abstract”. To say that a concept or form is “abstract” is to say that it is only a partial definition. Hegel describes the moment of understanding, for instance, as abstract (EL §§79, 80) because it is a one-sided or restricted definition or determination ( section 1 ). Conversely, a concept or form is “concrete” in the most basic sense when it has a content or definition that it gets from being built out of other concepts or forms. As we saw ( section 2 ), Hegel regarded Becoming as the first concrete concept in the logic.

Although Hegel’s writing and his use of technical terms can make his philosophy notoriously difficult, his work can also be very rewarding. In spite of—or perhaps because of—the difficulty, there are a surprising number of fresh ideas in his work that have not yet been fully explored in philosophy.

• [EL], The Encyclopedia Logic [Enzyklopädie der philosophischen Wissenschaften I] . Because the translations of EL listed below use the same section numbers as well as sub-paragraphs (“Remarks”) and sub-sub-paragraphs (“Additions”), citations simply to “EL” refer to either translation. If the phrasing in English is unique to a specific translation, the translators’ initials are added.
• [EL-BD], Encyclopedia of the Philosophical Sciences in Basic Outline Part I: Science of Logic [Enzyklopädie der philosophischen Wissenschaften I] , translated by Klaus Brinkmann and Daniel O. Dahlstrom, Cambridge: Cambridge University Press, 2010.
• [EL-GSH], The Encyclopedia Logic: Part 1 of the Encyclopaedia of Philosophical Sciences [Enzyklopädie der philosophischen Wissenschaften I] , translated by T.F. Geraets, W.A. Suchting, and H.S. Harris, Indianapolis: Hackett, 1991.
• [LHP], Lectures on the History of Philosophy [Geschichte der Philosophie] , in three volumes, translated by E.S. Haldane and Frances H. Simson, New Jersey: Humanities Press, 1974.
• [PhG], Phenomenology of Spirit [Phänomenologie des Geistes] . Because the translations of PhG listed below use the same section numbers, citations simply to “PhG” refer to either translation. If the phrasing in English is unique to a specific translation, the translator’s initial is added.
• [PhG-M], Hegel’s Phenomenology of Spirit [Phänomenologie des Geistes] , translated by A.V. Miller, Oxford: Oxford University Press, 1977.
• [PhG-P], Georg Wilhelm Friedrich Hegel: The Phenomenology of Spirit [Phänomenologie des Geistes] , translated and edited by Terry Pinkard, Cambridge: Cambridge University Press, 2018.
• [PR], Elements of the Philosophy of Right [Philosophie des Rechts] , edited by Allen W. Wood and translated by H.B. Nisbet, Cambridge: Cambridge University Press, 1991.
• [SL-dG], Georg Wilhelm Friedrich Hegel: The Science of Logic [Wissenschaft der Logik] , translated by George di Giovanni, New York: Cambridge University Press, 2010.
• [SL-M], Hegel’s Science of Logic [Wissenschaft der Logik] , translated by A.V. Miller, Oxford: Oxford University Press, 1977.
• Aristotle, 1954, The Complete Works of Aristotle: The Revised Oxford Translation (in two volumes), edited by Jonathan Barnes. Princeton: Princeton University Press. (Citations to Aristotle’s text use the Bekker numbers, which appear in the margins of many translations of Aristotle’s works.)
• Fichte, J.G., 1982 [1794/95], The Science of Knowledge , translated by Peter Heath and John Lachs, Cambridge: Cambridge University Press. (Citations to Fichte’s work include references to the volume and page number in the German edition of Fichte’s collected works edited by I.H Fichte, which are used in the margins of many translations of Fichte’s works.)
• Kant, Immanuel, 1999 [1781], Critique of Pure Reason , translated and edited by Paul Guyer and Allen Wood. Cambridge: Cambridge University Press. (Citations to Kant’s text use the “Ak.” numbers, which appear in the margins of many translations of Kant’s works.)
• Plato, 1961, The Collected Dialogues of Plato: Including the Letters , edited by Edith Hamilton and Huntington Cairns. Princeton: Princeton University Press. (Citations to Plato’s text use the Stephanus numbers, which appear in the margins of many translations of Plato’s works.)
• Bencivenga, Ermanno, 2000, Hegel’s Dialectical Logic , New York: Oxford University Press.
• Berto, Francesco, 2007, “Hegel’s Dialectics as a Semantic Theory: An Analytic Reading”, European Journal of Philosophy , 15(1): 19–39.
• Burbidge, John, 1981, On Hegel’s Logic: Fragments of a Commentary , Atlantic Highlands, NJ: Humanities Press.
• Düsing, Klaus, 2010, “Ontology and Dialectic in Hegel’s Thought”, translated by Andrés Colapinto, in The Dimensions of Hegel’s Dialectic , Nectarios G. Limmnatis (ed.), London: Continuum, pp. 97–122.
• Findlay, J.N., 1962, Hegel: A Re-Examination , New York: Collier Books.
• –––, 1966, Review of Hegel: Reinterpretation, Texts, and Commentary , by Walter Kaufmann. The Philosophical Quarterly , 16(65): 366–68.
• Forster, Michael, 1993, “Hegel’s Dialectical Method”, in The Cambridge Companion to Hegel , Frederick C. Beiser (ed.), Cambridge: Cambridge University Press, pp. 130–170.
• Fritzman, J.M., 2014, Hegel , Cambridge: Polity Press.
• Harris, Errol E., 1983, An Interpretation of the Logic of Hegel , Lanham, MD: University Press of America.
• Harris, H.S. (Henry Silton), 1997, Hegel’s Ladder (in two volumes: vol. I, The Pilgrimage of Reason , and vol. II, The Odyssey of Spirit ), Indianapolis, IN: Hackett).
• Hyppolite, Jean, 1974, Genesis and Structure of Hegel’s “Phenomenology of Spirit ”, Evanston, IL: Northwestern University Press.
• Inoue, Kazumi, 2014, “Dialectical Contradictions and Classical Formal Logic”, International Studies in the Philosophy of Science , 28(2), 113–132.
• Jaśkowski, Stanislaw, 1999 [1969], “A Propositional Calculus for Inconsistent Deductive Systems”, translated by Olgierd Wojtasiewicz and A. Pietruszczak, Logic and Logical Philosophy (7)7: 35–56. (This article is a republication, with some changes, of a 1969 translation by Wojtasiewicz entitled “Propositional Calculus for Contradictory Deductive Systems (Communicated at the Meeting of March 19, 1948)”, published in Studia Logica , 24, 143–160.)
• Kaufmann, Walter Arnold, 1965, Hegel: Reinterpretation, Texts, and Commentary , Garden City, NY: Doubleday and Company Inc.
• –––, 1966, A Reinterpretation , Garden City, NY: Anchor Books. (This is a republication of the first part of Hegel: Reinterpretation, Texts, and Commentary .)
• –––, 1976 [1972], “The Hegel Myth and its Method”, in Hegel: A Collection of Critical Essays , Alasdair MacIntyre (ed.), Notre Dame, IN: University of Notre Dame Press: 21–60. (This is a republication of the 1972 Anchor Books/Doubleday edition.)
• Kosok, Michael, 1972, “The Formalization of Hegel’s Dialectical Logic: Its Formal Structure, Logical Interpretation and Intuitive Foundation”, in Hegel: A Collection of Critical Essays , Alisdair MacIntyre (ed.), Notre Dame, IN: University of Notre Dame Press: 237–87.
• Lauer, Quentin, 1976, A Reading of Hegel’s “Phenomenology of Spirit” , New York: Fordham University Press.
• Margolis, Joseph, 2010, “The Greening of Hegel’s Dialectical Logic”, in The Dimensions of Hegel’s Dialectic , Nectarios G. Limmnatis (ed.), London: Continuum, pp. 193–215.
• Maybee, Julie E., 2009, Picturing Hegel: An Illustrated Guide to Hegel’s “Encyclopaedia Logic” , Lanham, MD: Lexington Books.
• McTaggart, John McTaggart Ellis, 1964 [1910], A Commentary of Hegel’s Logic , New York: Russell and Russell Inc. (This edition is a reissue of McTaggart’s book, which was first published in 1910.)
• Mueller, Gustav, 1958, “The Hegel Legend of ‘Synthesis-Antithesis-Thesis’”, Journal of the History of Ideas , 19(3): 411–14.
• Mure, G.R.G., 1950, A Study of Hegel’s Logic , Oxford: Oxford University Press.
• Pinkard, Terry, 1988, Hegel’s Dialectic: The Explanation of a Possibility , Philadelphia: Temple University Press.
• Priest, Graham, 1985, “Inconsistencies in Motion”, American Philosophical Quarterly , 22(4): 339–346.
• –––, 1989, “Dialectic and Dialetheic”, Science and Society , 53(4): 388–415.
• –––, 1997 [2006], In Contradiction: A Study of the Transconsistent , expanded edition, Oxford: Oxford University Press; first edition, Martinus Nijhoff, 1997.
• Popper, Karl R., 1940, “What is Dialectic?”, Mind , 49(196): 403–426. (This article was reprinted, with some changes, in two different editions of Conjectures and Refutations: The Growth of Scientific Knowledge , listed below.)
• –––, 1962, Conjectures and Refutations: The Growth of Scientific Knowledge , New York: Basic Books.
• –––, 2002, Conjectures and Refutations: The Growth of Scientific Knowledge , second edition, London: Routledge Classics.
• –––, 2013, The Open Society and its Enemies , Princeton: Princeton University Press. (This is a one-volume republication of the original, two-volume edition first published by Princeton University Press in 1945.)
• Rosen, Michael, 1982, Hegel’s Dialectic and its Criticism , Cambridge: Cambridge University Press.
• Rosen, Stanley, 2014, The Idea of Hegel’s “Science of Logic” , Chicago: University of Chicago Press.
• Singer, Peter, 1983, Hegel , Oxford: Oxford University Press.
• Solomon, Robert C., 1983, In the Spirit of Hegel: A Study of G.W.F. Hegel’s “Phenomenology of Spirit” , New York: Oxford University Press.
• Stace, W.T., 1955 [1924], The Philosophy of Hegel: A Systematic Exposition , New York: Dover Publications. (This edition is a reprint of the first edition, published in 1924.)
• Stewart, Jon, 1996, “Hegel’s Doctrine of Determinate Negation: An Example from ‘Sense-certainty’ and ‘Perception’”, Idealistic Studies , 26(1): 57–78.
• –––, 2000, The Unity of Hegel’s “Phenomenology of Spirit”: A Systematic Interpretation , Evanston, IL: Northwestern University Press.
• Taylor, Charles, 1975, Hegel , Cambridge: Cambridge University Press.
• Wandschneider, Dieter, 2010, “Dialectic as the ‘Self-Fulfillment’ of Logic”, translated by Anthony Jensen, in The Dimensions of Hegel’s Dialectic , Nectarios G. Limmnatis (ed.), London: Continuum, pp. 31–54.
• Westphal, Kenneth R., 2003, Hegel’s Epistemology: A Philosophical Introduction to the “Phenomenology of Spirit” , Indianapolis, IN: Hackett Publishing Company.
• Winfield, Richard Dien, 1990, “The Method of Hegel’s Science of Logic ”, in Essays on Hegel’s Logic , George di Giovanni (ed.), Albany, NY: State University of New York, pp. 45–57.

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• Hegel on Dialectic , Philosophy Bites podcast interview with Robert Stern
• Hegel , Philosophy Talks preview video, interview notes and recorded radio interview with Allen Wood, which includes a discussion of Hegel’s dialectics

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• Published: 30 May 2024

The link between ancient microbial fluoride resistance mechanisms and bioengineering organofluorine degradation or synthesis

• Randy B. Stockbridge   ORCID: orcid.org/0000-0001-8848-3032 1 &
• Lawrence P. Wackett   ORCID: orcid.org/0000-0002-3255-1101 2  

Nature Communications volume  15 , Article number:  4593 ( 2024 ) Cite this article

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• Applied microbiology
• Bioremediation
• Environmental biotechnology
• Metabolic engineering

Fluorinated organic chemicals, such as per- and polyfluorinated alkyl substances (PFAS) and fluorinated pesticides, are both broadly useful and unusually long-lived. To combat problems related to the accumulation of these compounds, microbial PFAS and organofluorine degradation and biosynthesis of less-fluorinated replacement chemicals are under intense study. Both efforts are undermined by the substantial toxicity of fluoride, an anion that powerfully inhibits metabolism. Microorganisms have contended with environmental mineral fluoride over evolutionary time, evolving a suite of detoxification mechanisms. In this perspective, we synthesize emerging ideas on microbial defluorination/fluorination and fluoride resistance mechanisms and identify best approaches for bioengineering new approaches for degrading and making organofluorine compounds.

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Introduction.

Early humans harnessed organic compounds, transition metals, and salts, but they largely avoided fluorine until the nineteenth century. At that time, chemists known as the “fluorine martyrs” experimented with fluorine gas and hydrogen fluoride, ultimately to the detriment of their health 1 . The first nucleophilic halogen exchange reaction to introduce fluorine into an organic molecule was carried out by the chemist and composer Aleksandr Borodin in 1862 2 . After Henri Moissan was awarded the 1906 Nobel Prize in Chemistry for methods to more safely handle fluorine, organofluorine chemistry blossomed. Another marked uptick in fluorine chemistry occurred in the 1940s and 1950s, as a direct consequence of the Manhattan Project and the need to enrich uranium as the hexafluoride, bringing the field to its current state 3 . Today thousands of fluorinated compounds have entered commerce 4 , 5 . For example, over the last 22 years, more than 50% of newly registered pesticides are organofluorine compounds 6 . Another prominent class of organofluorine compounds is designated as PFAS, standing for per- and poly-fluoroalkyl substances. We will use PFAS broadly here to refer to per- and polyfluorinated compounds, particularly those with -CF 2 - and -CF 3 functionality.

Over the last ~80 years, PFAS has become widely used because of their high degree of chemical stability, lower boiling points than compounds of comparable mass, and propensity to form a fluorous phase characterized by immiscibility in water and typical organic solvents 7 . These properties make them ideal as heat exchange agents, fire-fighting foams, water repellents, non-stick agents, and chemically resistant polymers. Combining perfluorinated alkyl chains with polar groups such as carboxylates, sulfonates, or amines generates amphiphilic molecules that serve as detergents and surface active agents. While the precise number is constantly changing due to pressure for replacement, there are still more than one thousand PFAS compounds in current commercial use.

Research on PFAS distribution and toxicity has raised alarm about their environmental persistence 3 , their accumulation in blood serum and tissue 8 , and their physiological effects 9 , 10 , leading to stringent environmental regulations for certain PFAS 11 . Globally, almost the entire human population has detectable blood serum levels of PFAS 8 , in major part due to environmental exposure from water or food sources 12 . Organofluorine contamination has emerged as one of the most pressing environmental regulatory issues over the last five years, and it is expected that regulatory constraints will extend to more compounds, highlighting the necessity for PFAS and organofluorine remediation and replacement.

Currently, remediation and replacement efforts largely use physical and chemical methods 13 , 14 . However, increasingly urgent calls for mitigation worldwide have generated intense interest in finding novel, sustainable ways to reduce or minimize exposure to PFAS and organofluorine pollution 15 , 16 , 17 , 18 . It is within this context that the first microbial solutions to PFAS contamination are advancing. These fall into two major categories: (1) remediation of contaminants, for example, treatment of concentrated PFAS waste in bioreactors, or perhaps highly contaminated natural systems, and (2) biotechnology to develop high-performance organofluorine chemicals with a lower fluorine content than some current commercial PFAS. As an example of the growing interest in such biosynthetic approaches, a consortium funded by the European Commission, consisting of eight academic institutions, and industry and manufacturing entities, recently embarked on a major effort to develop fluorinated polymer precursors biologically in order to replace their chemical synthesis ( https://www.sinfoniabiotec.eu ). In addition, two other applications in the biosynthesis of fluorinated compounds are for generating fast-decaying 18 F-isotope labeled molecules for Positron Emission Tomography (PET) 19 and specifically fluorinated natural products such as antiviral agents 20 .

Microbial approaches to address organofluorine pollution have several advantages. Bioremediation would be cheaper and more effective than physico-chemical remediation in some circumstances if suitable biological systems can be identified or engineered. Likewise, biologically-generated replacement chemicals could be designed to have less toxicity and greater biodegradability. Enzymatic synthesis of fluorinated organic molecules has the potential to make tailored structures that are difficult to make via conventional synthesis 20 .

In this Perspective, we focus on the microbial physiology that underlies these promising biological approaches for solving problems related to organofluorine persistence. In particular, organofluorine degradation yields fluoride ions, and biological syntheses use NaF. Though NaF is much safer for humans than HF and fluorine gas, fluoride is highly toxic to the bacteria carrying out biosynthetic or biodegradation reactions 21 , 22 . We will review how these applications have been thwarted by the toxicity of fluoride for bacteria, and present a perspective on how this problem might be overcome. We argue that applying fundamental physiological considerations to bioengineer solutions to PFAS and organofluorine persistence can help circumvent some of the common roadblocks that have emerged in these fields of study.

An overview of microbial organofluorine metabolism

Naturally evolved fluorinated natural product metabolism.

Fluorine is more common in the earth’s crust than phosphorus, nitrogen, and sulfur and yet a survey of the elemental composition of several dozen prokaryotes did not identify fluorine amongst the 33 elements found, making it less prevalent than non-biological metals like cadmium, tin, and silver 23 . Although most microbes and plants have evolved to minimize fluorine assimilation, very few have harnessed fluorochemistry (Fig.  1 ). Plants of several varieties in Australia, Africa, and South America produce fluoroacetate to deter feeding by animals, since the compound becomes highly toxic to central metabolism after metabolic conversion to fluorocitrate 24 , 25 . Fluoroacetate production is thought to be an ancient function given the geographic and taxonomic distribution of the fluoroacetate producers. Even fewer organisms make other monofluorinated natural products, for example, 4-fluoro-L-threonine 26 or fluorinated fatty acids 27 , which are also toxic metabolite mimics, and the fluorinated antibiotic nucleocidin 28 .

Left, During the pre-Anthropocene era of life, covering ~3.8 billion years, fluorine in the form of fluoride anion (F − ), derived largely from minerals, exhibited toxicity to cells and protocells by binding to Mg 2+ and Ca 2+ centers in enzymes or ribozymes. Fluoride export functions arose early in evolution. Today, most living things avoid fluorine, but a few rare plants and prokaryotes naturally evolved to biosynthesize fluoroacetate as a metabolic toxin to kill competitors and predators. Right, In the last 100 years and into the Anthropocene, humans have exposed the biosphere to a tsunami of inorganic and organic fluorine compounds. Of greatest concern are the large number of per- and polyfluorinated compounds (PFAS), such as perfluorooctanoic acid (PFOA) and 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid (GenX), shown at the top right. PFAS are persistent in the environment, raising human and ecosystem health concerns.

Enzymatic degradation of organofluorines

Naturally evolved defluorinase enzymes are inherently rare given the scarcity of fluorinated natural products, such as fluoroacetate described above 29 . The early discovery of a bacterial fluoroacetate dehalogenase belonging to the α/β-hydrolase superfamily 30 spurred additional discovery efforts for fluoroacetate dehalogenase activity within this family 31 . More recently, members of the haloacid dehalogenase-like hydrolase (HAD) superfamily have also been shown to catalyze the defluorination of fluoroacetate to yield glycolic acid and HF 32 . These fluoroacetate dehalogenases prefer fluorine over other halogen substituents, suggesting that they were selected for fluoroacetate detoxification or assimilation of fluoroacetate as a carbon source 30 , 33 . The X-ray structure of fluoroacetate dehalogenase from Rhodopseudomonas palustris revealed a highly specific and compact binding site for the fluorine atom of the substrate, which is suggested to significantly enhance catalytic C–F bond cleavage 34 .

In most cases, canonical fluoroacetate dehalogenases exhibit little to no activity with α,α-difluoro carboxylic acids characteristic of many PFAS chemicals of interest to remediate. However, several defluorinases that act on difluoroacetic acid have been discovered recently, holding open the possibility that naturally evolved enzymes might be able to degrade longer chain α,α-difluoro acids 35 . The enzyme products of difluoroacetic acid defluorination are two fluoride anions and an α-keto acid. Since α-keto acid decarboxylases are known, a plausible degradative pathway for perfluorocarboxylic acids would use consecutive paired reactions of α,α-defluorination and decarboxylation, releasing fluoride ions at each step and culminating in trifluoroacetic acid, an end product that is highly recalcitrant to further degradation.

Other enzymes with defluorination activity have also been identified, although it is less clear that these evolved naturally for the purpose of C–F bond cleavage. For example, 2 or 4-fluorobenzoate serves as a substrate for the anaerobic growth of bacteria that also grow on the common natural substrate benzoate 36 . Defluorination during 4-fluorobenzoate metabolism was shown to occur following ring reduction, catalyzed by the enoyl-CoA hydratase/hydrolase that participates in benzoate assimilation 37 . However, in these cases, defluorination is considered to be a promiscuous enzyme activity 38 . Likewise, a number of oxygenases have been demonstrated to support growth on fluorinated alkanes and aromatics in addition to naturally abundant substrates 38 , 39 . In other cases, oxygenases have been shown to participate in a non-growth dependent, promiscuous release of fluorine from fluorinated alkanes 40 , alkenes 41 , and aromatics 42 , 43 . The reactions typically proceed through the formation of gem -fluoro alcohols that undergo spontaneous elimination of HF.

Biological systems that degrade perfluorinated compounds have also been reported recently 44 , 45 , including reports of the defluorination of perfluorinated acids in consortia 46 , 47 , 48 and by a single bacterium 49 . While no enzymes were directly identified in those studies, the reactions are proposed to be reductive based on the identity of the products and gene expression studies 50 . Most recently, the electron bifurcating caffeoyl-CoA reductase system of Acetobacterium spp. was implicated in the reductive defluorination of perfluorinated unsaturated carboxylic acids 51 .

Bioengineering organofluorine synthesis to replace PFAS

With more than 200 applications and thousands of individual chemicals in commercial use 7 , PFAS utilization will continue for the foreseeable future. However, there are intense efforts underway in industry and academia to replace the most problematic compounds with more lightly fluorinated analogs 20 , 21 , 22 . Current fluorination reactions often use HF or other hazardous reagents, and regio-selective synthesis of partially fluorinated compounds is difficult 52 . Many fluorinating reagents used in organic synthesis are toxic and highly unstable in water. There is a need for better control and safety in organofluorine synthesis. In this context, an emerging area of organofluorine synthesis research is on biosynthetic approaches that use enzymes to carry out fluorination chemistry and perform reactions in aqueous solutions.

It would be ideal to prepare specific fluorinated molecules using simple fluoride salts, such as NaF or KF. Nature offers the enzyme fluorinase, which catalyzes the reaction of fluoride anion and S-adenosyl-L-methionine (SAM) to make 5′-fluoro-5′deoxyadenosine (5′-FDA) and L-methionine 53 . Initially identified in the fluoroacetate-producing bacterium Streptomyces cattleya , the fluorinase reaction thus uses fluoride ion to make a C–F bond and is the main entry point for fluorine in the production of the natural products fluoroacetaldehyde, fluoroacetate, and 4-fluoro-L-threonine 54 . However, fluorinase also has limitations for biosynthesis, including low k cat values (up to 0.4 min −1 ) 55 and high K m values for fluoride (2 mM for the well-studied S. cattleya enzyme) 20 . Fluoride is a poor nucleophile in water due to the high free energy of hydration of the anion 56 , which must be overcome by the enzyme to catalyze a nucleophilic displacement reaction with SAM. A range of other fluorinase enzymes have been tested but so far, none show markedly different steady-state kinetic parameters 55 . Likewise, mutagenesis strategies have not significantly lowered the K m for fluoride 57 . Nonetheless, fluorinase has been successfully leveraged in biosynthetic pathways to produce a variety of simple organofluorines used as PET tracers and medical imaging agents 58 , 59 , 60 . Moreover, although fluorinases are rare, recent research has uncovered new and more diverse enzymes than previously known 55 . It is likely that ongoing research into the structure/function relationships of these enzymes will continue to support advances in fluorine biocatalysis in the near future. In addition, there is evidence that other types of enzymes can act as entry points for fluorine into organic molecules, for example, those that contribute to the synthesis of omega-fluoro oleic acid 61 , which presumably originates from fluoroacetyl-CoA, or the fluorinated nucleoside antibiotic nucleocidin 62 . Additional research on these rare enzymatic chemistries will be essential to advance the biosynthesis of PFAS replacement chemicals.

Fluoride stress is a key challenge for organofluorine metabolism

Earlier studies on biological organofluorine synthesis and degradation strongly indicate that fluoride anion toxicity is a major impediment to progress in both fields of study 21 , 55 , 63 , 64 . Unlike other monovalent anions like chloride, fluoride inhibits essential enzymes in central metabolism, often by forming tight complexes with metallo-cofactors like calcium or magnesium within the enzyme’s active site 65 . The fluoride inhibitory constants ( K i values) for enzymes like enolase (which catalyzes the penultimate step in glycolysis), pyrophosphatase, and various kinases are typically in the range of 100 μM 66 . Congruent with this, WT bacteria mount a gene expression response at intracellular fluoride concentrations around 60 μM 67 , and extracellular concentrations as low as 200 μM 68 .

Fluoride toxicity becomes particularly acute in the context of organofluorine bioremediation and biosynthesis. While studies that establish microbial degradation of PFAS are still in the early days, many research groups are searching for PFAS-degrading microorganisms, since microbial processes are more easily applied in scenarios with dilute PFAS that preclude technologies that rely on PFAS capture and concentration. Some commercial PFAS molecules contain 15 or more fluorines, and due to this atom’s electronegativity, C–F bond cleavage by any mechanism releases fluorine as a fluoride anion. Because fluoride cannot passively diffuse across the membrane, if this reaction occurs in the cytoplasm, fluoride will accumulate intracellularly. The intracellular volume of a typical bacterial cell is on the order of a femtoliter 69 – in other words, if one femtomole of PFAS enters a cell and undergoes one C–F bond cleavage, the fluoride concentration will approach 1 M. In a hypothetical scenario of environmental PFAS degradation, a cell will approach toxic levels of intracellular fluoride (>100 μM) upon uptake and defluorination of perfluorooctanoic acid from just 10 pL of medium contaminated with 1 ppb of this substance, a value that is observed in PFAS-polluted environmental samples 70 . We have measured enzymatic C–F bond cleavage in one instance to be as fast as 10 bonds cleaved per second per enzyme (and there are thousands of enzymes per cell). Thus, for bacteria metabolizing such polyfluorinated compounds, PFAS or organofluorine degradation will rapidly release enough fluoride to impact cellular physiology. Moreover, fluoride produced intracellularly and released, or produced in the periplasm, readily re-enters and accumulates in cells via a process called weak acid accumulation 65 , 71 , especially as the medium pH acidifies, which is typical with dense bacterial cultures. For cultures of P. putida engineered to grow on fluorinated substrates, fluoride accumulates in the medium to concentrations exceeding 50 mM 63 . Similarly, the synthesis of PFAS alternatives by bacteria involves substantial fluoride stress, since the microbe must take up fluoride in a controlled manner as a substrate for synthesis. The mM K m values of fluorinase for fluoride require that cells tolerate intracellular fluoride levels 100-fold greater than those that begin to elicit fluoride stress responses.

Observations from naturally evolved and engineered microbes highlight the biological challenges inherent to fluoride use. In E. coli , high concentrations of fluoride stall cell division and growth, which is only resumed after fluoride is removed 71 . Organisms that have evolved natural fluorination capabilities, like S. cattleya , separate growth and energy metabolism from organofluorine biosynthesis, only expressing fluorinases in stationary phase 72 , 73 . In an engineered strain of Pseudomonas putida expressing a defluorinase enzyme and grown on α-fluorocarboxylic acids, fluoride stress limits the growth rate 63 . Similarly, for Acetobacterium spp. that catalyze reductive defluorination of perfluorinated unsaturated carboxylic acids, strains that lacked a functional fluoride export protein failed to perform defluorination, linking fluoride detoxification and enzymatic defluorination 51 .

Biosynthetic reactions require circumventing bacteria’s fluoride defenses to deliver fluoride in a controlled manner. For example, biosynthesis of fluoroacetate in E. coli requires not only the biosynthetic genes from S. cattleya , but also chromosomal knockouts of the crcB gene, which encodes a fluoride channel 64 . Likewise, fluoroacetate synthesis in P. putida KT2440 was achieved by harnessing natural fluoride response elements to deliver fluoride to the cells in a controlled manner 55 .

Microbial fluoride stress responses: recent advances

Although perfluorinated organic compounds are an anthropogenic stressor, fluoride resistance mechanisms are ancient and diverse (Fig.  2 ). Fluorine in the earth’s crust is largely found as fluoride bound in mineral form, for example: fluorite, fluorapatite, topaz, cryolite, sellaite, and villiaumite 74 . Fluorite (CaF 2 ) is a mineral mined for fluorine extraction to make PFAS and other industrial fluorine-containing compounds. In acidic waters, in particular, fluoride can be extracted from minerals. Soil, seawater, and surface water typically possess fluoride concentrations in the tens-to-hundreds of micromolar concentration range 75 , which is high enough to elicit a biological response 67 . Thus, biological systems have been exposed to toxic levels of the anion over evolutionary time.

Pink spheres represent F − , orange triangles represent PO 4 − , and gray spheres represent Ca 2+ . Most bacteria exhibit a subset of these responses. (1) Flouride export is the first line of defense against environmental fluoride, which usually enters the cell via weak acid accumulation at low pH (bottom right). Bacteria typically encode one of the two types of fluoride exporters: Fluc ( crcB ) or CLC F . (2) Fluoride-responsive riboswitches are widespread among bacteria, upregulating the expression of genes involved in fluoride resistance. These bind fluoride as a Mg 2+ -fluoride complex. Other unknown mechanisms of gene regulation also exist. (3) Weak acid accumulation of fluoride reduces the proton-motive force and decreases the cytoplasmic pH, which cells counteract by expressing Na + /H + antiporters. Fluoride-acclimated microbes exhibit enduring changes in pH homeostasis. (4) Various microbes overexpress inorganic pyrophosphatase, other phosphatases, and phosphate importers. This might be partly to surmount inhibition of phosphoryl transfer enzymes by fluoride, but it has also been shown that phosphate protects cells from fluoride stress. (5) Fluoride and divalent cations like Ca 2+ and Mg 2+ form poorly soluble complexes, which alters divalent metal ion homeostasis. Divalent cation transporters are overrepresented in operons with fluoride export proteins. (6) Fluoride inhibits several glycolytic enzymes, notably enolase, decreasing intermediates in lower glycolysis and the TCA cycle. Bacteria respond to this inhibition in various ways, including overexpression of glycolytic enzymes, metabolic shift to anaerobic fermentation, or pausing metabolism and growth. (7) As a consequence of the perturbations to oxidative metabolism and metal ion homeostasis, many microbes mount an oxidative stress response when fluoride levels are high. (8) Although less well understood as part of a natural fluoride response, some bacteria are able to synthesize minerals, such as fluorapatite (shown), with lattices that incorporate fluoride and effectively sequester this ion, intra- or extracellularly. (9) Many microbes exhibit changes in extracellular phenotypes like adhesion, biofilm formation, cell membrane structure and integrity, and polysaccharide export upon fluoride stress.

Environmental fluoride enters cells largely as HF 71 . With a pK a value of 3.4, appreciable HF is formed in niches with a pH below ~7. HF is membrane permeant but dissociates to H + and F − at the physiological cytoplasmic pH. The ionic form becomes trapped in the cell, accumulating to levels dictated by the pH gradient across the membrane 71 . Via this process, even low levels of environmental fluoride can breach the cell and evoke a cellular stress response. Our understanding of these responses, which include fluoride export, modulation of pH and ion homeostasis, and metabolic rewiring, continue to advance (Fig.  2 ). We argue that by exploiting fundamental microbial physiologies — in particular fluoride stress responses — we can unlock better strategies for biodegradation or biosynthesis of organofluorine molecules such as PFAS. Although this review focuses on bacteria, fluoride stress responses are ancient and conserved, at least in part, among microorganisms. Thus, physiological fluoride responses in yeast and fungi will also be examined.

Fluoride export

Across the tree of life, the first lines of defense against fluoride toxicity are membrane exporters that maintain this anion at low cytoplasmic concentrations 65 . Among bacteria, two fundamentally different fluoride export proteins have been identified, the CLC F s (gene name may be annotated sycA , eriC , clcA , clcB ) and the Flucs (gene name may be annotated crcB or fluC ) 65 . A survey of bacterial genomes from the Joint Genome Institute’s GEBA set of representative prokaryotic genomes 76 shows that >85% of strains in the collection possess a fluoride exporter (Fig.  3 ). Species that lack fluoride exporters tend to be obligate intracellular symbionts with reduced genomes, for example members of the genera Tenericutes, Spirochetes , and Fusobacteria . The widespread distribution of these fluoride export genes among microbes emphasizes the pervasive impact of environmental fluoride over evolutionary time. The CLC F and Fluc proteins are usually mutually exclusive in bacterial genomes; only ~3% of strains surveyed possess both. The importance of these exporters to fluoride resistance has been demonstrated in diverse organisms (Table  1 ).

Genomes are from a phylogenetically representative genomes set curated by the Joint Genome Institute (GEBA dataset, Genomic Encyclopedia of Bacteria and Archaea, bacterial genomes only) 76 . At right are the exporter distributions for four major bacterial phyla, with phylogenetic branch lengths according to ref. 134 .

The CLC F s are fluoride/proton antiporters that harness the proton gradient to expel fluoride from the cytoplasm 77 . These proteins are members of the large CLC (“ c h l oride c hannel”) family of anion transporters and channels, which are found in all kingdoms of life. Biochemical experiments have demonstrated that CLC F s are >80-fold selective for fluoride over chloride, the halide that is closest in size and the main biological anion 77 , 78 . Fluoride-specific CLC F s can be identified based on three signature sequences: the GNNLI/GMGLI in the N-terminal domain that defines ion selectivity, GREGT/V at the heart of the transport machinery, and the GEVTP sequence in the C-terminal domain that contributes fluoride-binding residues 77 , 78 , 79 . Among the major bacterial phyla, CLC F s are found most frequently in Bacteriodetes (~30% of species) and Firmicutes (~20% of species). Many bacteria also possess additional CLC homologs for chloride transport; these are not capable of transporting fluoride 80 .

In contrast to the CLC F s, the Flucs ( Flu oride c hannel) function as passive fluoride channels 81 that exploit the positive-outside membrane potential (the electrical component of the proton-motive force) to drive the expulsion of this anionic species 71 . The Flucs are notable for their rapid rate of F − efflux (10 6  ions/s) and extremely high selectivity for fluoride over other anions, which exceeds 10,000-fold 81 , 82 . The Flucs are the most selective ion channel yet described, and no role besides fluoride export has been ascribed to any protein in this family 65 . The Flucs assemble as unusual antiparallel dimers, where one protomer is inserted into the membrane facing out, and the other is inserted into the membrane facing in 81 , 83 . Fluc proteins can be encoded by single genes, in which case a single protomer is inserted into the membrane in both inward and outward-facing conformations, assembling as an antiparallel homodimer, or they can be encoded by paired genes that express to form heterodimers of obligate inward- and outward-facing subunits 84 . Typically, the genes for the heterodimeric Flucs are adjacent to each other in genomes, and both genes are required for fluoride efflux activity 84 . Heterodimers are more common than homodimers among Gram-positive bacteria. Heterodimers are considerably rarer in Gram-negative phyla, which primarily express Flucs as homodimers.

Yeast, fungi, plants, and some ocean-dwelling animals like corals and sponges also possess fluoride exporters that belong to a third molecular family known as FEX 85 , 86 . FEX proteins are related structurally to the Flucs but possess a more complex two-domain fold 83 , 87 . Like the Flucs, these proteins export fluoride via a channel mechanism driven by the membrane potential 87 .

Although the fluoride exporters contribute most to fluoride resistance, different organisms still exhibit substantial variability in the fluoride concentrations that they tolerate (Table  1 ), suggesting that there are additional physiological determinants of fluoride resistance. In one illustration of the potential contribution of these additional fluoride resistance mechanisms, fluoride-acclimated strains of Saccharomyces cerevisiae exhibited a 700-fold gain in fluoride resistance, independent of fluoride export 88 .

Fluoride-responsive gene regulation

Many bacteria exhibit a multilayered response to fluoride ions that is controlled at a genetic level. The best-studied regulatory element is the fluoride riboswitch, which binds fluoride as a fluoride-magnesium complex and upregulates the transcription of downstream genes 67 , 89 . Indeed, extensive riboswitch-based regulation is used by S. cattleya and Methylobacterium DM4 , microbes capable of synthesizing and degrading fluorinated compounds, respectively 72 , 90 . As detailed below, a number of genes associated with microbial fluoride resistance are controlled by riboswitches. The most common proteins found in operons with these riboswitches are the fluoride exporters 67 , although only ~15% of Flucs and ~30% of CLC F s are regulated by riboswitches. While some fluoride response genes are constitutively expressed 71 , other unknown regulatory mechanisms also exist. For instance, in Streptococcus mutans , which do not possess a fluoride riboswitch, CLC F expression is induced by fluoride addition to the medium 68 . A fluoride-resistant strain of S. mutans exhibits a constitutive expression of the CLC F genes, and a single nucleotide polymorphism in the intergenic region 5′ to the operon was linked to this mechanism 91 .

pH and ion homeostasis

Fluoride stress and pH homeostasis are intimately linked. Since membrane permeation of the weak acid HF is the major route to fluoride accumulation in the cytosol 92 , fluoride exposure is correlated with cytoplasmic acidification 21 . In addition, fluoride export is dependent on the proton-motive force – either as an explicit chemical driving force for the CLC F s, or as a component of the electrical gradient, as for the Flucs. As a result, maintaining pH homeostasis is important for fluoride resistance in microorganisms, and acid stress-response pathways are commonly upregulated in response to fluoride 88 , 93 . Indeed, after fluoride exporters, the next-most common class of riboswitch-associated genes is Na + /H + antiporters 67 , which contribute to pH homeostasis in bacteria 94 . In fluoride-acclimated S. cerevisiae , one of the most frequent physiological adjustments was tolerance to lower homeostatic pH 88 .

There is also evidence that phosphate homeostasis is linked to fluoride resistance. The gene encoding pyrophosphatase is among the genes most frequently associated with fluoride riboswitches 67 , and in various organisms, including Enterobacter cloacae FRM 95 , Acidithiophilus ferredoxins 96 , and S. cerevisiae 97 , the expression of pyrophosphatase, polyphosphatase, and phosphate importers has been functionally linked to fluoride resistance. In addition, genes annotated as haloacid dehalogenases are often associated with riboswitches 67 . These were initially assumed to be related to fluorine metabolism, but it has since been shown that the majority of enzymes with the haloacid dehalogenase fold are in fact phosphoesterases 31 , 98 . This association between fluoride exposure and phosphatase upregulation might reflect overexpression to counteract inhibition of phosphoryl transfer enzymes by fluoride 99 . But there is also evidence that increased cytoplasmic phosphate is protective against fluoride toxicity 88 , 97 , perhaps partly due to phosphate’s buffering capacity at neutral pH.

In addition to phosphate importers and Na + /H + antiporters, genes encoding other ion transporters are also overrepresented in fluoride-related operons and gene expression analyses 95 . Fluoride chelation impacts ion homeostasis, especially for divalent cations, and these perturbations can contribute to oxidative stress. The fluoride-related expression of ion transporters might thus be a response to fluoride-induced changes to divalent metal availability.

Metabolic acclimation to fluoride

Fluoride-stressed microorganisms enact substantial, but sometimes dissimilar, changes to metabolism. While fluoride exerts broad-spectrum inhibition on any enzyme that relies on metal-ATP complexes, the enzymes of glycolysis are particularly sensitive. Enolase (which converts 2-phosphoglycerate to phosphoenolpyruvate, or PEP) is inhibited by fluoride with a K i value of ~80 μM 100 . In P. putida , this is reflected by the accumulation of metabolites in upper glycolysis, and the depletion of PEP and other downstream products, including TCA cycle intermediates 21 . For some bacteria, the response to enolase inhibition by fluoride is to simply make more of the enzyme. Enolase is often observed in operons controlled by fluoride riboswitches 67 , and in fluoride-resistant E. cloacae FRM, enolase transcripts are upregulated 176-fold in response to fluoride 95 . Other bacteria, like E. coli , appear to shut down metabolism entirely, only resuming growth once the fluoride insult is removed 71 . For other bacteria, like S. mutans , there is evidence of a shift away from oxidative metabolism 101 . Formate hydrogen lyase, which oxidizes formic acid to produce ATP during anaerobic sugar fermentation, is another of the most common fluoride riboswitch-associated enzymes 67 . Fluoride-adapted S. cerevisiae also exhibit metabolic shifts to anaerobic fermentation pathways, and like P. putida , are depleted in TCA cycle intermediates 88 .

Correlations between amino acid pools and fluoride resistance have also been observed. For example, fluoride-stressed P. putida has elevated levels of methionine and tyrosine 21 . The gene encoding chorismate mutase, a key enzyme in the biosynthesis of aromatic amino acids, is one of the most common genes in fluoride exporter gene neighborhoods 67 , and its expression is upregulated in fluoride-resistant S. mutans together with the fluoride exporters in the same operon 91 . In this same fluoride-resistant S. mutans strain, pyruvate kinase, the enzyme that directs PEP towards pyruvate oxidation and the TCA cycle, is heavily mutated 91 , suggesting that other PEP-consuming biosynthetic pathways, such as aromatic amino acid production, might be favored under fluoride stress.

Oxidative stress responses

Stress-response pathways, especially oxidative stress responses, are activated in a broad cross-section of bacterial species upon fluoride challenge 21 , 88 , 95 , 97 , 101 . Oxidative stress is associated with a number of the primary effects caused by fluoride described above, including intracellular acidification and disruption to the membrane potential, disruption of divalent metal homeostasis, and arrest of oxidative metabolism. Response to oxidative stress might also rationalize the association between aromatic amino acids and fluoride resistance, as tyrosine has been proposed to mitigate oxidative stress 102 , 103 , 104 . In yeast, fluoride resistance is imparted by the export of compounds like nitrates that contribute to oxidative stress, and the import of antioxidant metabolites like sulfite 97 .

Cellular architecture, adhesion, and biofilm formation

In addition to the homeostatic and metabolic responses described above, fluoride exposure is also associated with changes to extracellular phenotypes. Genes associated with adhesion, biofilm formation, cell membrane structure and integrity, and polysaccharide export are upregulated in response to fluoride by diverse bacteria, including P. putida , S. mutans , S. sobrinus , and A. ferrooxidans 21 , 96 , 101 . Among the oral streptococci, fluoride has been shown to inhibit lectins that shape biofilm architecture 105 , and increase turnover of cell wall peptidoglycans, contributing to cellular lysis 106 . Similarly, changes to cell morphology, including cell shortening or lack of separation following septation, and increased extracellular carbohydrate content, are also caused by fluoride stress 63 , 107 , 108 . The influence of fluoride on cellular adhesive properties is also observed for eukaryotic microbes. Fluoride-acclimated S. cerevisiae exhibited increased clumping and mutations to genes associated with flocculation, pseudohyphal growth, cell surface properties, and adhesion 88 . In both prokaryotic and eukaryotic microorganisms, fluoride potentiates the effect of drugs that inhibit cell wall biosynthesis 109 , 110 , 111 .

Fluoride sequestration

Another mechanism of fluoride resistance is sequestration of the anion in an insoluble form, to avert its inhibition of metabolic enzymes. The molecular mechanisms of sequestration are currently not as well understood. It has been shown that some species, including the extremely fluoride-resistant Exiguobacterium indicum MLN15 and Bacillus licheniformis absorb fluoride in electron-dense granules on the surface and in the cytoplasm, respectively, although the molecular identity of these is unknown 112 , 113 . Bacteria are known to biomineralize calcium in crystal lattices that can incorporate fluoride, including francolite, aragonite, dolomite, and apatite 114 , 115 , 116 , 117 , 118 . Based on these principles, fluoride mineralization has been engineered into some bacteria 119 , 120 . In addition, evidence from eukaryotes suggests that fluoride sequestration is harnessed to counteract fluoride toxicity. For example, some plants accumulate fluoride as insoluble calcium or magnesium complexes in the vacuole 121 , and fluoride-acclimated yeast exhibited far lower soluble calcium compared to total calcium, suggesting calcium’s presence in an insoluble form 88 . Thus, sequestration can be used as a fluoride mitigation strategy by biology, and, in principle, could be stimulated by the divalent metal and phosphate uptake described above.

Recommendations for leveraging fluoride resistance

The carbon atoms in perfluorinated compounds are highly oxidized already and reductive defluorination coupled to ATP generation has not, to our knowledge, been demonstrated. The high degree of fluorination coupled with the lack of known metabolic energy provided by PFAS metabolism suggests that fluoride stress is a major constraint on sustained organofluorine biodegradation in engineered, and perhaps highly contaminated, natural systems. Likewise, fluoride tolerance is required for the synthesis of organofluorine chemicals, since fluoride ions must be supplied to bacteria for fluorination reactions. In addition to host tolerance, multiple enzymes, some of which use redox and other cofactors, must operate in conditions of fluoride stress. Intersecting approaches will be needed to overcome this problem, such as using or engineering fluoride-resistant bacterial strains, protein engineering to circumvent fluoride target sensitivity, or optimizing growth conditions to help mitigate fluoride stress. We expand on some of these ideas below.

Using naturally resistant cellular hosts

For some bacteria, like E. coli , fluoride accumulation is bacteriostatic, halting metabolism while fluoride is present 71 . Other bacteria, like Bacillus subtilis , Neisseria subflava , and Streptococcus species exhibit varying degrees of autolysis in response to fluoride stress 106 . Extreme fluoride challenges can cause complete lysis of the population 68 . Such species are obviously less suited for applications that require high fluoride levels. In contrast, some bacteria exhibit extreme fluoride tolerance, managing growth and metabolism even at high environmental fluoride concentrations. Such strains have been identified in the context of organofluorine biosynthesis 21 , biodegradation 63 and fluoride sequestration 113 .

Evolving or acclimating host cells to resist fluoride

Because so many fluoride resistance mechanisms involve rewiring metabolic pathways to circumvent inhibition of glycolysis, cytoplasmic acidification, or oxidative stress, adaptive evolution or fluoride acclimation has the potential to rapidly generate strains with better fluoride tolerance. We are not aware of any systematic investigation of fluoride acclimation in bacteria, but the example of S. cerevisiae is encouraging, as fluoride acclimation over multiple generations yielded strains with ~700-fold better fluoride resistance, independent of fluoride exporter expression 88 . However, it should be noted that one natural mechanism of fluoride resistance is metabolic deactivation, which may be at odds with the end goal of improving fluoride resistance in order to metabolize fluorinated substrates.

Thus, a more relevant application of adaptive evolution might be to drive improved fluoride stress management and defluorination rates simultaneously 35 , 63 . Recent studies show that using fluorinated compounds as the sole carbon source generates dual and opposite selective pressures for sufficient carbon metabolism to provide cellular metabolites and ATP, counterbalanced by toxicity from excessive intracellular fluoride flux 35 , 63 . This combination of metabolic needs pitted against the requirement to handle fluoride stress is an ideal problem to solve by adaptive evolution. In a comparable case, a Pseudomonas strain was adapted to metabolize high levels of cytotoxic hydroxycinnamic acids from lignin breakdown 122 . Adaptive evolution allows natural selection to solve the problem of high internal fluoride levels, and these strains may find utility for both PFAS biodegradation and biosynthesis.

Engineering fluoride resistance

By engineering host bacteria, fluoride resistance could be further improved. Most straightforwardly, genes that are critical to the fluoride stress response, such as fluoride exporters, could be constitutively expressed. During PFAS biodegradation, the release of fluoride anion intracellularly can cause cessation of energy metabolism before a fluoride stress response is mounted 63 . Constitutive expression of fluoride exporters is one naturally evolved response that improves bacterial fluoride tolerance 91 . It is also possible that the expression of multiple fluoride exporters could help improve fluoride resistance. Each of the two mechanistically distinct fluoride export proteins has its own advantages, at least in principle. The F − /H + antiport mechanism couples fluoride export to the proton gradient, sustaining a lower intracellular fluoride concentration at equilibrium, whereas fluoride channels have the advantage of more rapid fluoride removal that does not depend on a proton gradient. However, it is at least theoretically possible that at high external fluoride, if a cell is unable to maintain a membrane potential, a fluoride channel could permit fluoride influx. Protein-level regulation could prevent this outcome. Although synthetic proteins that inhibit fluoride channels have been developed 123 , 124 , 125 , they have not been tested in biological systems, and no such natural regulatory mechanism has been identified. Fluc channels are more widely distributed among diverse bacteria than CLC F transporters (Fig.  3 ), and Flucs are found more commonly in strains that resist high fluoride or that use fluoride for synthesis. These observations perhaps imply that channels are biology’s favored solution to fluoride export.

We can also follow the example of nature and simply overexpress enzymes like enolase that represent key roadblocks in metabolism, those that respond to oxidative stress, or that, like pyrophosphatase, have homologs that are less sensitive to fluoride inhibition 126 . For bioremediation, the introduction of genes that contribute to external sequestration may be protective in static natural or engineered bioremediation systems in which exported fluoride might accumulate and reenter cells. One recent study showed that calcium carbonate precipitate generated by Pseudomonas sp. HXF1 could sequester fluoride in the form of CaF 2 and Ca 5 (PO 4 ) 3 F and diminish fluoride in groundwater 127 .

Growth conditions that reduce fluoride stress

The natural mechanisms that microbes use to withstand fluoride toxicity suggest several straightforward ways to optimize growth conditions, including maintaining the medium at neutral pH, providing phosphate and divalent cations in the medium, or supplementation with antioxidant compounds like sulfites. Accumulation of fluoride released by PFAS degradation might prove particularly acute in, for example, an engineered bioreactor designed to degrade concentrated PFAS waste. In this situation, fluoride toxicity could be ameliorated by including a solid-phase adsorbent material to sequester fluoride following its export into the extracellular space. A variety of fluoride-binding materials have been developed for treating potable waters that naturally contain high levels of fluoride 128 . Examples include bone char, activated carbon, activated carbon with metals, and more advanced ceramic materials containing rare earth metals.

For biosynthetic applications, it may prove possible to supply bound fluoride in a slow-release form to maintain a sub-toxic, steady-state level of fluoride. One example would be the amendment of biocatalytic reaction mixtures with fluorophosphate, which could be released by phosphatases 129 . However, there is a measurable background rate of non-enzymatic fluorophosphate hydrolysis and so more stable, but inexpensive, fluoride salts like BF 4 − could be efficacious in this regard.

Integrating fluorobiosynthesis with fluoride tolerance

Finally, fluorobiosynthesis pathways themselves could be engineered to reduce the cellular fluoride burden. Similar to organisms that naturally produce organofluorine compounds 72 , temporal separation of metabolism and biosynthesis could be used in engineered systems. Alternatively, fluoride-inhibited energy metabolism could be circumvented using bacteria capable of accessing electrons from electrodes, a process particularly useful to drive reductive defluorination 130 . In addition, the discovery, characterization, and engineering of new fluorinase enzymes should focus on the discovery of enzymes with lower K m values to reduce the intracellular fluoride required for synthesis. Orthogonal improvements to organofluorine biosynthesis pathways, like SAM regenerating systems, could also reduce the metabolic burden of fluorination chemistry, permitting high fluxes under conditions of low metabolic throughput. A SAM regenerating system has been developed for the purpose of supporting in vitro cobalamin biosynthesis and this could be useful in fluorinase biochemistry, too 131 .

Summary and outlook

PFAS accumulation in the environment is an expanding societal problem, and microbial bioengineering shows promise for PFAS remediation or synthesis of less-fluorinated and more biodegradable chemicals to replace undesirable PFAS. Much attention within this field has been directed towards the discovery or engineering of enzymes that can break the famously strong C–F bond. Progress along this front is promising: although such enzymes are rare, recent studies show that they are more diverse than previously thought 51 , and advancements in metagenomic sequencing and protein engineering will support future discovery and optimization of organisms, genes, and pathways that support organofluorine synthesis and degradation. For example, homologs to a newly discovered reductive defluorinating enzyme system were recently identified in metagenomes found on six continents, greatly expanding the range of enzymes of this type to be studied 51 . Furthermore, we argue here that defluorination chemistry is only a part of the challenge in this field. By acquiring a deep understanding of the fundamental microbial physiologies — in particular the fluoride stress responses — that support biodegradation or biosynthesis of organofluorine molecules, we can better harness ancient fluoride resistance mechanisms to address this very contemporary biochemical problem. Box  1 describes targeted areas of research that will further advance these fields.

Box 1 AREAS FOR FUTURE RESEARCH

Continued discovery and engineering of enzymes and metabolic pathways capable of efficient fluorination or defluorination.

Identify mechanisms of fluoride stress management that govern cell metabolism and viability in diverse bacterial hosts using multi-omics approaches.

Optimize regulation of fluoride tolerance mechanisms, including regulation of fluoride export activity.

Differentiate fluoride channels versus antiporters for high-level fluoride resistance under different metabolic circumstances.

Continued discovery and improvement of enzymes that reduce fluoride stress or that are insensitive to fluoride inhibition.

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Acknowledgements

The authors thank Carla Peralta for assistance in analyzing the distribution of fluoride exporters in GEBA genomes. R.B.S. is supported by the National Institutes of Health grant R35 GM128768. L.P.W. is supported by a grant from MnDRIVE Industry and the Environment Program.

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Stockbridge, R.B., Wackett, L.P. The link between ancient microbial fluoride resistance mechanisms and bioengineering organofluorine degradation or synthesis. Nat Commun 15 , 4593 (2024). https://doi.org/10.1038/s41467-024-49018-1

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