Rationalists say that reason is the source of ultimate truth or logic. Reason is absolute but if reason is absolute then won't defending it through reason be a circular reasoning? Like you can't defend religion through religious books. Then how can reason be defended by reason? How can experience be defended by experience itself?

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    Maybe there is no "absolute".... maybe we cannot define "reason"... We cannot define everything: we have to start somewhere. Commented Jul 14, 2022 at 6:43
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    By saying "reason is ultimate truth", I assume you are getting at the position that logic is infallible in some sense. If that's what you mean, this position is as common among empiricists as among rationalists, so it is not a rationalist position. Rationalism is the position that we have innate knowledge of some sort about the natural world; that we can't know everything we know just from experience. Commented Jul 14, 2022 at 7:23
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    See Münchhausen trilemma for more clarification... Commented Jul 15, 2022 at 3:42
  • Rationalists do not say that reason is the ultimate truth, it does not even qualify for being true/false. They say that reason is the way to get from one truth to another, but it can just as easily produce more falsehoods out of initial falsehoods. As for the initial truths, including those about the powers of reason itself, they appeal to some extra ingredient, "natural light", "intellectual intuition", pragmatic/empirical success, or whatnot.
    – Conifold
    Commented Jul 15, 2022 at 6:13

4 Answers 4


You are implying that a thing of a kind and another thing of a kind being involved in a logical argument makes it circular. This is not the case.

Circular reasoning is when you start with the premise you are attempting to prove. For example, you might begin with the premise "rationality is valid." If you then performed some logical operation and produced the conclusion "rationality is valid" then that would be circular reasoning.

Rationality as such is collection of a large number of concepts. When you use one of those concepts in a logical argument, you are using that concept. You are not using the collection, you are using a member of that collection. If you used some items from the collection rationality to prove some other item from the collection, that is not circular reasoning.

Confusing the collection rationality with items in the collection is a category error.

Using one religious book to support another religious book (not simply a copy or derivative book) is not circular reasoning. (It may involve other issues that affect the validity of the argument, but not circularity.) Using one experience to support the trust we place in another experience is not circular reasoning. (Again, we may be deluding ourselves, but the fault is not circularity.) Using one item to support another item of the same type is not circular reasoning.

There is, potentially, a very different logical fallacy that might be involved. That has been called "the stolen concept." That is, requiring the truth of the something that you are simultaneously trying to disprove.

Or, to express the idea of "the stolen concept" in another way: it involves using the truth of a claim to conclude the falsity of a claim.

So, consider the idea of logically disproving the validity of logic. Using logical proofs implicitly assumes the validity of logical proofs. Thus, a candidate logical proof that disproves the validity of logic is denying one of the implicit premises that the proof itself is based on. If such a situation arises, one should check the correctness of the candidate logical proof.

  • Or, one should stop trying to saw off the branch on is sitting on.
    – Scott Rowe
    Commented Jul 15, 2022 at 10:37

Rationality and rationalism are two different things.

  • Rationality has many definitions depending on the domain (economic, psychology, etc) but let's settle on a bare-bones definition: the belief that logic works.

It's pretty much a given, because if we don't believe that logic works at all, then we can't even conclude that this implies we can't reason, and we're kinda stuck. Note believing logic works does not imply believing humans are perfectly rational creatures who act reasonably and logically all the time. We're definitely not that.

  • Rationalism is a philosophical theory that posits "reason alone is enough to produce truth." I'm simplifying, but you get the idea. Quoting Wikipedia:

In an old controversy, rationalism was opposed to empiricism, where the rationalists believed that reality has an intrinsically logical structure. Because of this, the rationalists argued that certain truths exist and that the intellect can directly grasp these truths. That is to say, rationalists asserted that certain rational principles exist in logic, mathematics, ethics, and metaphysics that are so fundamentally true that denying them causes one to fall into contradiction. The rationalists had such a high confidence in reason that empirical proof and physical evidence were regarded as unnecessary to ascertain certain truths – in other words, "there are significant ways in which our concepts and knowledge are gained independently of sense experience".[4]

Different degrees of emphasis on this method or theory lead to a range of rationalist standpoints, from the moderate position "that reason has precedence over other ways of acquiring knowledge" to the more extreme position that reason is "the unique path to knowledge"

These paragraphs describe rationalism as spanning a wide spectrum, from moderate to completely insane.

Moderate rationalists would admit that, starting from a set of axioms that are assumed true, reason alone can produce propositions whose truth depends on the truth of the initial axioms. This sounds about right. It works well, especially in math, where it is made explicit that axioms are axioms, ie considered true in the context of the discipline, but unprovable. It works well in physics, where experimental evidence shows both the validity of the axioms and the domain over which they are reasonably valid and useful approximations of the real world. In fact, it works in every domain that is either purely abstract, or in concrete domains where the axioms can be shown to be reasonably true... by experiment, which then makes it a mix between rationalism and empiricism.

Extreme rationalists though... they simply make an additional step: they drop the essential matter of "the truth of everything derived from a set of axioms depends on the truth of the initial axioms". As long as you keep this essential bit, it's all a game, a thought experiment, but if you drop it, that's when trouble begins. Then they construct a whole theory from these "true" axioms. This goes on for as long as it has to, until the theory becomes complex and convincing enough on its own to obfuscate the fact that no-one knows if the base axioms are actually true. Then circular logic happens: after working on a theory for long enough, until they're convinced it is true, the rationalist simply... rationalizes that their base axioms must be true. This is easy, because they picked a set of axioms that they were fond of, either by pure intuition, as a direct result of their psychological orientation, or to serve a political purpose, or "it felt right, it must be so". That's where it goes horribly wrong. See: communism.

Most of the material in this extreme rationalist flavor of philosophy is a great way to learn about how people with problems in their heads rationalize that they're in fact right about everything. At the end of it, there is only narcissism, because what it boils down to is "if I think it, then it is so." The shining example standing above the crowd would be Rousseau, who abandoned his children to die in an orphanage, then wrote a book about how to raise and educate children.

Let's summon Descartes:

From the indubitability of the self, Descartes inferred the existence of a perfect God; and, from the fact that a perfect being is incapable of falsification or deception, he concluded that the ideas about the physical world that God has implanted in human beings must be true. The achievement of certainty about the natural world was thus guaranteed by the perfection of God and by the “clear and distinct” ideas that are his gift.

That's a great example of pure extreme rationalism: unprovable foundations, elaborate circular reasoning, and a conclusion that makes the author feel special. I don't see any reason to have any mercy. Let's not forget that Descartes was also involved in the Rosecroix cult, through which he had received the Illumination. Apparently "universal doubt" does not apply to occult rituals.

Rationalists have been at war with the empiricists for millenia, with no truce in sight.

Engineers and (real) scientists stand in the middle: "nice theory, let's test it."

If you catch a rationalist at a party, here's an amusing experiment you can do. Simply tell them,

"Did you know that, in order to turn a bicycle to the right, you have to turn the handlebars in the opposite direction?"

This one is fun because it is highly counter-intuitive.

If the guy owns a heavy powerful motorbike, or is a mechanical engineer, he'll just answer "yup, that's counter-steering, crazy isn't it?"

But if someone's axioms are "the bicycle will go where the front wheel points to because logic" then they won't get it. Which is ironic, because the reason you have to turn the handlebar in the opposite direction to initiate a turn is... precisely because the bicycle will go where the front wheel points to.

So your rationalist will come up with many reasonings to explain why it can't be true because it contradicts his basic axioms.

The next step is of course to put the rationalist on a bicycle. That won't work, because even people who rode bikes for years, and have been counter-steering for years, don't know they've been doing it. With a heavy motorbike, you have to do it on purpose. But a bicycle is light enough that you can do it without knowing.

So, in the interest of science, you tell the rationalist to push the left handle towards the front. This turns the handlebar clockwise ("to the right") and... the bike turns to the left, in the opposite direction.

Then it becomes an illuminating experiment about how our brains just can't process something if we "know" it can't be true. You will get all sorts of answers, my favorite being "of course it turned left, I pushed the left handle" (thereby ignoring the handlebar did in fact turn in the opposite direction of where the bike went).

If you have a true rationalist on your hands, then to make them understand that it's happening, you have to come up with a credible explanation why it's happening. That may involve changing some of their axioms. But if there's no logical justification, they won't believe it's happening. Even if it's happening right in front of them.

Don't elect rationalists.

  • I wouldn't want to elect an empiricist either, because we need to know in advance what will work. I would elect a wise person with experience. Excuse me, I need to pick up my lantern and go outside now.
    – Scott Rowe
    Commented Jul 15, 2022 at 10:34

"rationalists say that, reason is ultimate truth or logic. Reason is Absloute but if reason is Absloute then defending it through reason, won't be a circular reasoning?"

If I had to make the argument for rationality. My usual meta-take is "rationality is giving yourself the means to reach your goals". In that sense, and in my opinion, rationality is not rooted in logic, it is rooted in the world as we experience it. It turns out that in our world, logic- science- based thinking is the best tool we have to reach our goals. Thus these are the tools rationality leads us to use.

For the same reasons, rational thinking must include the irrational dimensions of humans, and for the same reasons rationality usually gives low value to "prayers and thoughts" since these have been shown (historically and scientifically) uneffective.

  • We keep track of not only what works, but what doesn't work, so that we don't have to stumble upon it again and again. Outside the US, anyway...
    – Scott Rowe
    Commented Jul 15, 2022 at 10:25

Isn't it rationality circular reasoning?

You probably mean Reason, rationality being the preeminence of Reason. In such case, you would be asking "Isn't it Reason circular reasoning?", which I think is your question.

Short answer: No, rationality/Reason is not circular: it is Logic that is circular. In the same form, communication is not circular: it is language that is circular.

Reason is the potential to think (produce judgements) according to a set of rules, the rules being what we know as Logic. Reason has no role on the assessment of the validity of judgements: reason just produce judgements.

"Circular reasoning" is a phenomenon in Logic that emerges when the rules that are used to validate some judgement are sustained on such judgement itself.

Having said that, according to many (e.g. Russell, Kant), Logic is in fact circular. The proof is trivial: any rule that could determine the validity of Logic will necessarily be logical. How otherwise the validity of Logic could be determined? All philosophy, including all sciences, are based on Logic, which is tautologically based on itself. Whenever a scientific discipline is considered valid, objective, accepted, the judgement "Logic is true (for no reason)" is implicitly assumed. Otherwise, not a single scientific discipline would be valid. Logic is necessarily and universally true.

The fact that Logic is circular does not imply a pejorative nature of the discipline. Logic and Mathematics are pure because of its circularity (see Kant's Transcendental Aesthetics for more on the tautological nature of knowledge).

In an equivalent way, communication is not circular. What is circular is the language (the dictionary is a circular set of definitions, all of them based on others). That doesn't make of language a fallacious resource.

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