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If philosophy is based on reason and rationality, then why is there so much disagreement?

Is it due primarily to operating with different premises absent consensus on their truth, so that dissenters tend to concede arguments are valid but disagree with the resulting conclusions?

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    First, much of philosophy is not based on "reason and rationality", existentialism, for example, and many philosophers are ambivalent about "reason and rationality" for good historical reasons, pardon the pun, see critical theory. And second, reason and rationality are only as good as their inputs, garbage in garbage out, they are sterile on their own. Those inputs come from reflections on current knowledge, intuitions and value judgments, and those vary widely. Reasonable people can disagree. A lot.
    – Conifold
    Feb 14 at 21:57
  • Maybe useful Bernard Williams, Ethics and the Limits of Philosophy (Routledge, 1985): a "perfect" rational being can make correct arguments and assess evidence but always from the human point of view made of values, beliefs, concerns, that in turn can be weighed and discussed but... Feb 15 at 9:40
  • asking 'why' is asking for opinions. You might like to read "A Manual for Writers of Research Papers, Theses, and Dissertations" by Kate L. Turabian to start. Argumentation is the way to exchange ideas. Feb 15 at 12:21
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    The premise of the question is clearly wrong. There is no disagreement in philosophy! ;-) Feb 16 at 8:23
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    Your first mistake is assuming that reason and rationality are some type of truth instead of simply some type of framework that truth may or may not exist on —just lie within reason and rationalize everything you want to believe.
    – mchid
    Feb 16 at 12:41

19 Answers 19

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The short version is that argumentation requires premises and inferences to get to conclusions. Even if philosophers agree on a systematic approach to inference, let's call such agreement logic, the premises themselves are free to differ. Thus, we may all agree that anyone who commits a crime should be imprisoned, but we may disagree on who committed the crime. Thus two reasonable parties can both be rational and yet have different conclusions.

In the simple case of deduction, this difference is known as validity and soundness. One can have a very rational argument, but if the premises aren't true, then the conclusion is unsound. Of course, reason and rationality is much more than an act of deductive reasoning. Many of our justifications for our conclusions are non-inferential in nature, and rather rely on some sort of subjective and immediate experience that differs from that of others. Thus, if among my premises include a distinction between red and green, and my opponent cannot experience such a distinction because of colorblindness, it is fair that my opponent reject my argument since they are unable to justify a premise about the distinction (without then falling into an argument about the nature of experience and colorblindness).

A final example of a source of disagreement is that logic itself might differ in the minds of philosophers. For instance, in classical logic, we might insist that the law of non-contradiction is applied in an argument. And yet, this "law" itself is a value, and not a fact. Notions of contradiction (See this answer on how contradiction may or may not be used (PhilSE in argumentation). So, perhaps under one circumstance, a philosopher might use classical logic, and in another, the philosophers might require a non-classical logic. Another philosopher is free to disagree about that sort of application of logic.

So, there are many reasons philosophers might disagree, but there are three obvious examples: different beliefs that serve as premises in argumentation, different sorts of justification and application thereof, and disagreement over what logic is and how to use it. This sort of complexity ensures that philosophers disagree, and that's because human beings are not duplicated, deductive engines, but rather philosophers are diverse in mind and body, and have a wildly divergent set of beliefs and methodologies to do philosophy itself, a subject studied by metaphilosophy.

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    There's also too many people intending to use philosophy to force a conclusion that didn't come from reason in the first place.
    – Joshua
    Feb 15 at 21:58
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It has been said man is a rational animal.
All my life I have tried to find evidence that could support this.

Bertrand Russell

While in the above, Russell takes aim at logic and the rational, he didn't spare philosophers either:

I've made an odd discovery. Every time I talk to a philosopher I feel quite sure that happiness is no longer a possibility. Yet when I talk with my gardener, I'm convinced of the opposite.

Ok Russell didn't say philosopher but savant. But for our purposes it's close enough for why philosophers tend to be disagreeable

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I see two big reasons for this:

  1. Lack of precisely defined terms. Take for instance the innocent little term "existence". Fundamental to many philosophies, but there are quite a few different interpretations in use out there. For instance, some only use it for things that exist within the real world. These people deny any existence to the natural numbers. Then there's mathematicians who'd say that they exist simply because they've defined them. And then there's the conundrum with existence in fictional worlds: While he does not freak me out in the least, Lord Voldemort is very much real within the Harry Potter universe. He exists within our heads just as much as natural numbers do. It's a whole, big can of worms. Nevertheless, philosophers often take their own intended meaning of the terms for granted, without providing thorough definitions, leading to all kinds of confusion and disagreement. And sometimes a philosopher may inadvertently shift from one definition to another within their own works, leading to even more confusion.

  2. Lack of rigor in the reasoning. If philosophers were rigorous, their works would sound exactly like mathematical proofs. And there would indeed be no debate about whether a certain conclusion was sound. Either, people would accept a conclusion, or they would point out a flaw within the proof, forcing the author to either retract or correct their work. Sometimes finding such a flaw will disprove the validity of the proof entirely, more frequently it will simply say that more work is needed to finish the proof.

As you might have realized by now, this is precisely a description of how mathematicians handle their arguments, or rather avoid getting into arguments. They precisely define their terms, and they compute their conclusions with rigorous reasoning in a way that even an undergrad can point to an error within their proofs and say "this is wrong" with confidence, should they find such an error. (This might require a lot of work from the student, making them a better mathematician in the process, but it's a rather mechanical kind of work that just takes a bit of dedication.) This is not the case within philosophy for the two reasons above.


Example for exercise:

  • One cat has one more tail than no cat.

  • No cat has two tails.

  • Therefore, one cat has three tails.

What are the implicit definitions of the terms involved? And how do they invalidate the reasoning presented?

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    Nothing is better than great sex. Bad sex is better than nothing. Therefore, bad sex is better than great sex.
    – Bumble
    Feb 16 at 10:00
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    @Bumble The PG rated version works just as well. Feb 16 at 11:38
  • @cmaster-reinstatemonica "in a way that even an undergrad can point to an error" If only that was true. Feb 24 at 11:02
  • @Speakpigeon Ok. I should have added "in principle". The problem is, that advanced proofs tend to use advanced terminology that's taken to be known by the reader. An undergrad student would need to look up each and every one of the terms that they do not know yet, and check whether the things that the proof does with these terms are all valid. Nevertheless, once they have done this work thoroughly (and thus become more proficient themselves) they will be able to point to any error they found and say "this is wrong because ..." with confidence. Feb 24 at 13:15
  • @cmaster-reinstatemonica "look up each and every one of the terms that they do not know yet" Yes, exactly, but what does not come out in what you say is that very many proofs relies on more basic proofs, each one involving yet more vocabulary to understand. So, in principle, may be, but in practice, very rarely, if ever. Feb 24 at 17:15
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Rationality consists in taking facts into account and arguing logically about them using a common language.

The problem is not philosophy, or philosophers, it is that different people will inevitably have diverging beliefs as to what are the facts.

This is inevitable simply because everyone have their own distinct vantage points on reality, this because two people cannot at the same time occupy the same location in space.

So we disagree about at least some facts, but we may be able to reconcile each other's points of view if we reason logically from the facts on which we are able to agree.

So arguing consists usually in an effort of one side to prove to the other side that their view is somehow contradicted by at least one of the facts on which the two sides both agree.

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Reason and rationality underpin life generally, yet disagreements are rife. Consider politics and economics, for instance: you would not last long in either field if you could not apply reason, yet both are notorious for disagreement.

If you study philosophical disagreements (there are many examples on this site!) you will find most of them arise from one or more of the following factors:

Different beliefs. We all come to philosophy with our own personal set of beliefs. Some people, for example, believe in God and absolute morality, while others consider belief in God to be a delusion and morality to be invented by societies. People with different beliefs are always likely to disagree about matters that effectively hinge on faith.

Vagueness of language. No matter how hard we try, we cannot eliminate ambiguity from what we say, so every time we attempt to convey a point to another person, particularly about abstract or nuanced matters, there is a strong likelihood of disagreement. This difficulty is intractable because of the circular nature of the definition of abstract ideas. Take the word 'exist' for example. You will find that it has a number of meanings, some of which are inherently vague, as a consequence of which you will find no-end of fruitless discussion about whether this that or the other thing 'exists'.

Fallacies. There are many subtle ways to make a mis-step in developing or following an argument, so cases arise in which people reach different conclusions because one or both of them has made some nuanced slip in their reasoning which neither have spotted.

Conjecture and plausibility. Much of philosophy concerns matters that cannot be decided by experiment. Different philosophers put forward different ways of thinking about some point, and whether you consider one to be more plausible than another is entirely a matter of taste and judgement.

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Apparently it is not enough to base a method on reason and rationality alone. These two are big words. Each philosopher subscribes that they name basic capabilities for doing the job. The dissense begins when spelling out the method on the next level of detail.

In science it is a successful method to start with a well-known problem. First one needs clear concepts to state the problem. Using these concepts as a tool science then develops a theory which will solve the problem and provide an explanation. Eventually one has to check whether the theory indeed solves the problem or at least, whether one has made some progress with the solution.

Philosophy is at risk to juggle with ill-defined concepts in empty space, without feedback from the given problem whether one is on track.

I agree with your proposal that the problem description should state explicitly also the premises of the enterprise

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One reason is that not everyone agrees philosophy is based on reason and rationality. There's a fairly large consensus around that idea, but there are significant outliers. For instance, most people would agree that Kierkegaard is an important philosopher. But he would have disagreed with the proposition that his philosophy is based on reason and rationality.

There's also disagreement on what reason and rationality actually mean. Plato, one of the acknowledged greatest philosophers of all time, was noted for his praise of reason and rationality. But many of the arguments he advances do not adhere strictly to what we might think of as rational argument. He arguably had a mystical view of "reason" that isn't entirely in line with what later thinkers meant by the term.

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Human language was never designed to convey the truth -- it can only describe how the truth appears from different angles. This puts the responsibility on the reader/listener to do the detective work and reconstruct the meaning, the truth behind words, using the words themselves as clues. This detective work is what we often fail to perform and that's why we often disagree -- we misinterpret the words of dead philosophers, most often by taking them too literally.

It's even worse when it comes to religious texts.

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I disagree. Science is the jugular vein of modern life. Science branched out of philosophy. Science is a gift of philosophy to humanity. There is not much disagreement in science. There are various other areas as well in which philosophy has contributed without much disagreement. For example ,modern day politics evolved under the heavy influence of philosophy.

Yes , there are also deep disagreements in philosophy because some fundamental understanding is missing. We have not yet grasped the nature of reality, we have not yet been able to define consciousness properly, we do not understand the workings of karma, we have no clue about God , we don’t know how to interpret quantum mechanics etc.

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I suspect there might be several factors that contribute:

  1. Vagueness: Many philosophical debates are over concepts that are so abstract that the meaning of the words or topics is not precisely defined, and it is not clear that they ever could be precisely defined. Many debates seem to suffer from confusion over the meaning of words, or slight differences in how the same word is being interpreted. (See also Wittgenstein.)

  2. Untestability: Many philosophical debates are over topics that can't be empirically tested. This eliminates a key self-correction mechanism to detect faulty thinking or to spot caveats and weak points in our arguments.

  3. Values and premises: People differ in their values, preferences, and in what premises and assumptions they are willing to accept. There's no reason to think we should all agree on matters of ethics and morals.

  4. Selection bias: In philosophy, you are most likely to be exposed to the topics where there is debate or disagreement. In some sense it is the debate that it is itself interesting. Once something becomes a fact that everyone agrees on, it ceases to be philosophy and is merely a fact. Or, if it is still considered a matter of philosophy, once everyone agrees on it, it is less likely to be discussed in textbooks, speeches, essays, debates, etc. Or, once it can be measured empirically, it becomes considered the domain of science rather than philosophy. So, in philosophy, you are more likely to be exposed to topics where there is debate, and less likely to be exposed to questions where there is wide agreement.

Why the field of philosophy in particular seem to suffer from these challenges, perhaps more so than other fields? I am not sure, but I can form several hypotheses:

  1. Generality: Perhaps because philosophy is driven to try to seek the most general questions, where topics are considered at the greatest level of generality and abstraction possible. Abstraction can lead to imprecision, as we try to group multiple concrete phenomena into a common pattern, and the concrete examples mostly fit the abstraction but not perfectly; abstraction can leads to vagueness; and abstraction can potentially lead to untestability.

  2. Tackling hard problems: Perhaps because philosophy prides itself on tackling problems that are beyond science and engineering and can't be answered by those methods, thereby inherently removing techniques that other disciplines have for eliminating disagreement (e.g., empirical testing).

  3. Ethics is subjective: Perhaps because philosophy often studies questions that are a matter of opinion or values ("should" rather than "is"), e.g., questions about ethics. Different values and premises will inevitably lead to different conclusions.

  4. Ambition: Perhaps because philosophy takes on some of the most important and challenging problems, problems that people care deeply about and have been wondering about for centuries and millenia. It's not reasonable to expect that we should reach universal agreement on those. Many other fields focus on what knowledge they can achieve with relatively high confidence; philosophy often pays attention to questions that matter, even if it's not clear how to attain high confidence in our answers.

See also https://paulgraham.com/philosophy.html for a provocative perspective that might be worth considering and might be worth contemplating one's individual response to.

Lastly, I want to issue a cautionary note about the temptation to view disagreement as "bad". Maybe it is a bad sign, but maybe it isn't. In many aspects of life, different perspectives and diversity of views make us richer. Two positions can be seemingly in opposition and yet both hold value to us. We can simultaneously read about reasons why free will might not exist and feel greater compassion towards those who are mired in poverty, addiction, suffering, etc., often partly or wholly for reasons beyond their control; and also read about reasons why we do have free will and feel inspired to better ourselves, make wise choices, and do great works. Philosophy often tackles subjects where there is no single truth, and diversity and differing perspectives can make our lives richer.

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    The reason philosophy is prone to these problems is because both science and religion have their orthodoxy over them. Philosophy (generally) doesn't -- because philosophers haven't come to a sufficient agreement to hold their own field. See also my answer to this question about power.
    – Marxos
    Feb 15 at 22:04
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    You say that abstractness leads to imprecision or vagueness and examples may mostly fit an abstraction but not perfectly. Abstraction on its own is not a cause of disagreements, as mathematics deals with very abstract concepts posed in great generality that can be very precisely described and admit many examples fitting their definitions perfectly. Mathematicians do not really disagree about what abstract concepts in math mean and century-old problems do reach universally accepted solutions. Look closer at the concepts philosophy is concerned with. Their mere abstractness should not be blamed.
    – KCd
    Feb 16 at 7:19
  • @KCd, Thank you for your feedback. It sounds like I have not clearly communicated the point I'm trying to make. I have revised my answer to try to state it more clearly. I changed "abstraction often leads" to "abstraction can lead". I know it is not a necessary consequence. Please also note that I am listing my best attempt at providing hypotheses. They might be wrong. [[Also, I want to provide you some feedback that "abstraction leads to imprecision or vagueness" is not what I wrote -- rather, I previously wrote "abstraction often leads to".]]
    – D.W.
    Feb 16 at 19:20
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There is disagreement because all inferences rely upon axioms that one cannot actually justify. In other words, all reasoning is based upon presuppositions that can never be proven as the Agrippa trilemma indicates.

As the wiki states,

If it is asked how any given proposition is known to be true, proof in support of that proposition may be provided. Yet that same question can be asked of that supporting proof, and any subsequent supporting proof.

And this continues ad infinitum until you accept a proposition ultimately on faith.

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The underlying reason is that the fundamentals are not clear:

  1. There is no consensus about how to discern what is true, let alone what is true.
  2. There is no consensus about how to argue.

It is no surprise that there is no consensus about any of the statements derived from these shaky foundations. Socrates brought that to the point with the shortest and most fundamental contradiction which, paradoxically, may be the most uncontroversial statement in philosophy:

Scio nescio.

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Since philosophy deals with abstract concepts, individual differences play an important role in this matter. Hence, the concepts people consider for analysis and their weightage are different. This causes disagreement. When the whole idea is considered by splitting into part by part, people feel their ideas make sense and they stick to them.

One can easily verify the idea I metioned first. Examine why identical twins argue alike even if their ideas are a bit irrational for others.

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Cognitive biases are factors within our subjective analysis of reality that may lead to perceptual distortion, inaccurate judgment, illogical interpretation, and irrationality. This may be the result of emotion, cognitive "shortcuts" and evolutionary adaptations, among other things.

Within philosophy, this could mean coming to different conclusions with respect to inductive or abductive reasoning (e.g. trying to decide what's the "best" conclusion based on the evidence, and the criteria for "best" may also more explicitly vary due to cognitive bias). These conclusions may, in turn, be used as premises in deductive arguments, which may lead to people accepting or rejecting those arguments.

Another element of this is whether we consider the deductive implications of some potential conclusion within abductive or inductive reasoning, along with the interplay of different conclusions. If that sounds complicated, consider this example: you see a live broadcast of someone somewhere and you conclude that they are there, and at the same time you see a live broadcast of them on the other side of the world, and you conclude that they are there. Individually, those conclusions may be justified. But taken together, they'd imply that the person can be at 2 places at once or that they're able to move faster than the speed of light. It would make more sense to conclude that one or both of those are pre-recorded, fake or involve look-alikes (even if you don't know which one).

Most deductive arguments follow one of a few simple forms, so for those sufficiently familiar with those forms (and invalid variants), they're probably not too likely to miss structural issues due to cognitive bias. The issue is more likely to be with the premises. Although there are also some fallacies that someone might miss, like equivocation, where you can have a seemingly valid structure with reasonable premises, but the premises may use different definitions of terms (e.g. "man" as in "the human race" or as in "male humans"), which would make the argument invalid.

There are also really complex deductive arguments, where it's much easier for a fallacy to be missed. One example is the ontological argument, which I've reviewed in detail at some point, but the argument is equivocating and essentially just comes down to defining God into existence, although it's hard to spot that given the complexity (... but maybe that's just my cognitive bias speaking).


Some disagreement may also be explained by the fact that we don't have complete information, there are just different ideas about what's actually true, and we may not have ways to resolve that.

We may also have different priorities and choose to frame things in different ways. Moral philosophy specifically may include some aspect of that. There's certainly some parts which say "morality is objectively like this" (whether that's "objective morality" or not), whereas some others may see a moral philosophy more as something they want, or something to strive towards, to try to make the world a better place, for example.

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It is because people disagree on premises, like other users have answered. however, why should they disagree on premises (like whether we saw GOD or a monkey when we open our human eyes for the first time)?

Are all premises equal? You don't find mathematicians disagreeing on premises that much. This suggests that they are not. In theory, logic and math could start on perhaps an infinitude of premises, but most of it would not resemble what we call math and logic now.

Most of our math and logic is centered around two main predicate declarators: "IS" and equals. These are used to declare (not merely conclude) what truth is. These create premises.

What surrounds these declarators are nouns: objects or ideas that have some kind of existence, like "A = A" (the identity axiom of math), but these are contestable. Does the "A" on the left really equal the "A" on the right? Are they not displaced in space and therefore different? Yes, but that premise is not used (for us human, anyway).

In the end, some argue that premises, since they can't be "proven", are merely an aesthetic of the believer. Yet, this is way to weak to explain 5000yrs of history of power or how engineering is holding up buildings for millennia.

The answer to this postmodern ennui is our shared history. Something began, perhaps at multiple points in Time, if you want, but, nonetheless, there is history and that biases our logic and math. Because the rest of the Universe shares this history, it works.

Except when it doesn't, like various conflicts which dominate our world right now and tear us apart. For this, you must do what your Creator commanded: Get on top of this world and hold dominion. Power is tearing our soul down and parasitizing all of our ideals/history. Or find me. I already did it and am waiting, with the plan of Earth.

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If philosophy is based on reason and rationality, then why is there so much disagreement?

Is it due primarily to operating with different premises absent consensus on their truth, so that dissenters tend to concede arguments are valid but disagree with the resulting conclusions?

  1. Not every individual is equally capable of reason and rationality.
  2. Lack of information. Lack of correct and valid answers to the fabric of reality and how it works. The "gap".
  3. Disagreement precedes advances in knowledge. What value is there in rehashing things known? 1+1=2. The Earth is round. Hydrogen is the lightest element. Nobody learns nuttin' that way !! Disagreement is almost essential to progress.
  4. Debate/disagreement can be competitive and we have some competitive genes.
  5. Imagine if there were none that would disagree, would we end up like lemmings, drowned in the sea? Or lined up sitting on wooden benches in churches donating a percentage of our earnings to an organization claiming they can provide individuals with eternal life?

Dissent and disagreement, reasonably explored, can invigorate and bring out the best in some.

At one of the rare meetings of a significant number of mental powerhouses that resulted in a photograph coined "the worlds smartest photograph"... the Solvay Conference in 1927... is well known to have been almost exclusively given to heated debate and discussion.

Solvay 1927

It's what smart people do when they are trying to figure out complicated shit that nobody ever figured out before.

What do logical rational people do when they want to advance knowledge??

Makes sense eh? Discussing things agreed upon advances nothing. Disagreement and debate is the path to knowledge.

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Philosophy is about studying the fundamental topics in life and human existence.

Logic is an important part of philosophy and one of its principal tools in exploring ideas and propositions.

But so are epistemology (the nature and meaning of human knowledge), ethics (what people ought/ought not do in relation to others) and metaphysics (existence, consciousness, space, time, theology).

Given the uncertainties pertaining to the latter three areas, any logic linking a proposition together will perforce be a bit fuzzy and there would be ample scope for disagreement - quite sharp disagreement in some cases.

You might compare your question with one submitted by a would-be physics student: if physics is all about math then why do we have so many theories about the essence of matter, isn't math the same wherever you are ?

Of course math is math yet we do have different theories of matter. Some are due to disagreement on the available knowledge (e.g. on the limitations and significance of experimental data), the unavailability of other knowledge that is essential for a determination, the impact of existing theories on the thinking of present-day theorists, social implications of a theory and so on. Apply the same math tools to different data selections and you will likely come up with different theories. There is also a share of peer rivalry in this field of study - as there must also be in the field of philosophy.

Philosophy is like the topic it seeks to comprehend - always imprecise, always reflective of both the subjective values of the observer as well as the more objective values of people generally.

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There is so much disagreement because there are so many people.

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    This is necessary but not sufficient. There is not nearly as much disagreement in mathematics, science, engineering, etc. for instance, and these fields involve large communities of people. Feb 16 at 20:41
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Philosophy is not based on reason and rationality. These are important elements but there are also other things equally important involved in philosophy: general and specific knowledge (logic, ethics, mind, etc.), personal reality and worldviews, etc.

Philosophy is not like science, where theories, hypotheses and facts are proven to be true or false. Philosophy does not offer proofs. It offers opinions, descriptions and explanations of how things are or work, and a knowledge of 3,000 years of human thought.

Now, opinions and worldviews are subjective. But even reasoning and logic may be used diversely. So, one can easily see why there is so much disagreement among philosphers. This disagreement dates from the ancient times.

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