It is well known that many Buddhist philosophers and scholars of various traditions, such as Nagarjuna and Chandrakirti rely on and acknowledge reductio ad absurdum as a method of positing arguments and discussing different forms of knowledge.

On the Wikipedia page regarding Buddhist logico-epistemology, it is stated:

K. N. Jayatilleke sees Buddha's epistemological view as a kind of empiricism which also includes a particular view of causation (dependent origination): "inductive inferences in Buddhism are based on a theory of causation. These inferences are made on the data of perception. What is considered to constitute knowledge are direct inferences made on the basis of such perceptions."[13]: 457  Jayatilleke argues the Buddhas statements in the Nikayas tacitly imply an adherence to some form of correspondence theory, this is most explicit in the Apannaka Sutta (MN 60).*He also notes that Coherentism is also taken as a criterion for truth in the Nikayas, which contains many instances of the Buddha debating opponents by showing how they have contradicted themselves.[13]: 352–353.  He also notes that the Buddha seems to have held that utility and truth go hand in hand, and therefore something which is true is also useful (and vice versa, something false is not useful for ending suffering).[13]: 359 

However, on that same page, it is stated:

According to Jayatilleke, 'pure reasoning' or 'a priori' reasoning is rejected by the Buddha as a source of knowledge.[13]: 273  While reason could be useful in deliberation, it could not establish truth on its own.

This is slightly confusing to me because if you are subscribing to some of the views mentioned in the first paragraph (and some other Buddhist concepts more generally), there is no way to defend them in a purely posteriori way. Thus, at least some apriori reasoning is necessary in order to even begin establishing other principles used throughout Buddhist philosophy and worldview which are considered truthful. Reductio ad absurdum is one such way of establishing truth in an apriori way.

As such, does Buddha see reductio ad absurdum as valid forms of argumentation and deriving truth, and if not, how does he argue for different concepts without relying on apriori reasoning?

I just want to clarify that in this case, I am saying "reductio ad absurdum" to mean the following: reductio ad absurdum argument is showing that non-acceptance of some X would result into a complete incoherence and any non-acceptance would simply not be sound and coherent, and hence, it necessarily must be accepted for anything other than its affirmation is not possible. In other words, non-acceptance of some X concept or idea would result in a self-refuting idea logical fallacy. And as noted above, it seems that Buddha subscribed to the notion that contradiction is not acceptable. So I think it would only make sense if Buddha affirmed reductio ad absurdum for there can be situations where anything other than embracing and accepting some idea X would result in complete incoherence, and this is technically done in an apriori and deductive manner but according to Jayatilleke, Buddha rejected apriori argumentation so it doesn't make much sense.

I hope that what I wrote is clear. I'm a beginner and interested in learning Buddhist concepts. If something I wrote is incorrect, please let me know and I will change it.

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2 Answers 2


All concepts which Buddha discusses are based on experience. There is no a priori reasoning involved. Buddha says come and experience yourself. All reasonings are rooted in experience. However there is “reductio ad absurdum” or proof by contradiction.

For example - Theory of Anatta or not-Self.

You do not begin by assuming Self. But you begin by asking , what is that which you call self ? Is it forms ? Or is it feelings ? Or is it perceptions? Or is it choices ? Or is it consciousness?

Then the question arises , Is form permanent or impermanent? Are feelings permanent or impermanent? Are perceptions permanent or impermanent? Are choices permanent or impermanent? Is consciousness permanent or impermanent?

The answer is ,impermanent ,for all the above because all conditioned phenomena are impermanent. It is an observed fact of existence which can be experienced by anyone.

Then we argue that , if form is impermanent then is it suffering or not ? If feelings are impermanent then is it suffering or not ? If perceptions are impermanent then is it suffering or not ? If choices are impermanent then is it suffering or not ? If consciousness is impermanent then is it suffering or not?

The answer is yes, it is suffering. If the answer is yes then is form , feelings , perceptions, choices and consciousness are worth calling Self?

The answer is no. Therefore all conditioned (and unconditioned) phenomena are not-self.

What we assumed as Self turns out to be not-Self.

  • Is not saying that "one should trust one's experience" itself an apriori idea, assuming that our experience is trustworthy? Isn't affirmation of non-contradiction an apriori idea? "All concepts which Buddha discusses are based on experience" Why can you trust such an experience? What if it never even happened? I'm curious as to how Buddhists answer such questions. In my view, these things need to be grounded in apriori-derived principles through reductio ad absurdum in order for anything posteriori to even be able to stand. I will look into this a bit more.
    – setszu
    Commented Dec 1, 2023 at 13:23
  • Oh and you never showed a source for your statements.
    – setszu
    Commented Dec 1, 2023 at 13:30
  • @setszu yes. One should trust one’s knowledge. Knowledge is gathered by experiencing reality. There is a consequence of knowing in terms of experience. You should trust the knowledge. If you can’t trust the knowledge then experience it yourself. Experience will teach you that Buddha is right. Knowledge is like a Sun which will arise no matter how dark the night is. Once knowledge is verified through experience you can built upon it. There is no need to assume anything, it will unravel itself. Commented Dec 1, 2023 at 13:33
  • "One should trust one’s knowledge" why? You didn't answer my questions regarding thing. "Once knowledge is verified through experience you can built upon it" - what about knowledge which is presupposed for verifying empirical knowledge, but can't be empirically verified itself? How does Buddhism deal with that? "There is no need to assume anything, it will unravel itself" - I mean, the whole point of apriori and deductive proofs is to not assume anything, but rather prove it, so that knowledge can be grounded in something and not collapse into incoherence and radical subjectivism.
    – setszu
    Commented Dec 1, 2023 at 15:48
  • Here is the definition of “a priori” -“A given proposition is knowable a priori if it can be known independent of any experience other than the experience of learning the language in which the proposition is expressed.” .Anatta reasoning is not a priori. It is based on experience. Buddha is all about experience. There is no knowledge without experience. However you can utilise others experience without getting into the trouble of verifying yourself. Commented Dec 2, 2023 at 3:03

I guess an example of "proof by contradiction" is in the 2nd or 3rd sutta, i.e. Anattalakkhaṇasutta (SN 22.59)

The Buddha said this:

“Mendicants, form is not-self. For if form were self, it wouldn’t lead to affliction. And you could compel form: ‘May my form be like this! May it not be like that!’ But because form is not-self, it leads to affliction. And you can’t compel form: ‘May my form be like this! May it not be like that!’

  • Hm, it might show that, but it's shown in a posteriori way (observation of form and experience of "self" and affliction), right? The question's focus is really on reductio ad absurdum argumentation in the context of apriori proofs. Having said that, application of this in a posteriori way might imply validity and necessary basis in an apriori way for it to even be applicable, so it might count???
    – setszu
    Commented Dec 1, 2023 at 13:29
  • I think the "a priori reasoning" is, our "self" is under our control, and if something is "self" then it is under our control. The observation is, form is not under our control. The conclusion or argument is, therefore it is not fit to view the form as self.
    – ChrisW
    Commented Dec 1, 2023 at 13:42
  • If your "philosophy" is meant to be entirely a priori, then I suppose Buddhism is more like a "science", in that its reasoning is based at least in part on "observation" or "experience".
    – ChrisW
    Commented Dec 1, 2023 at 15:34
  • 1
    It's not really what I'm saying. I'm saying that observation and experience rely on things which cannot be empirically proven, and thus must rely on apriori proofs. Empiricism must be grounded in proper apriori demonstrations for any of it to be valid. The argument you provided applies this logical principle (needs to be shown apriori) towards something observable (posteriori). This is not an issue as long as the structures which are used for demonstrating your posteriori conclusion are sufficiently demonstrated in an apriori way (which is really the only way for them).
    – setszu
    Commented Dec 1, 2023 at 15:44
  • 1
    Jayatilleke says that Buddha rejected apriori reasoning, but Buddha evidently used structures which can only be shown through apriori reasoning. In fact, Buddha implicitly affirms them IMO. I dont have access to his book, but the only way I can square this is to assume that by "apriori", Jayatilleke is talking about analytic apriori (to use Kant's language). Perhaps, Buddhas view is similar to Hume: "...there is an evident absurdity in pretending to demonstrate a matter of fact, or to prove it by any arguments a priori. Nothing is demonstrable, unless the contrary implies a contradiction."
    – setszu
    Commented Dec 1, 2023 at 15:54

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