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In the Wikipedia article Buddhist Logic, it is mentioned that Buddhist Logic is different from classical western logic.

‘Indian Logic’ should be understood as being a different system of logic than modern classical logic (e.g. modern predicate calculus), but as anumāna-theory, a system in its own right. ‘Indian Logic’ was influenced by the study of grammar, whereas Classical Logic which principally informed modern Western Logic was influenced by the study of mathematics.

How does Buddhist logic work then? And how is it used in the exegesis of Buddhist scriptures?

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    This is a very interesting article! aeon.co/essays/… – Ilya Grushevskiy Jan 3 '17 at 15:18
  • @IlyaGrushevskiy Could you repost that as an answer, please, instead of as a comment. – ChrisW Jan 3 '17 at 19:04
  • @IlyaGrushevskiy great article referred, thank you – Mishu 米殊 Jan 4 '17 at 5:04
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This article goes through the catuskoti - the fourfold statemnt of 'is, is not, both is and neither' - and attempts to put Buddhist logic into 20th century Western logical terms.

https://aeon.co/essays/the-logic-of-buddhist-philosophy-goes-beyond-simple-truth

The Buddha would not have accepted the three classical laws of logic imo:

The law of identity: 'X=X', is different from the Buddha's declaration of "treat this as this and that as that, not this as that and that as this". In other words, treat X as X, but don't axiomatically assume equality. (on a side note, 'X=X' is a tautology, and provides no information, so not a very useful rule when dealing with the perception of identity!)

The law of non-contradition is dealt with in the article really well, and the law of excluded middle, weeell - I think we can all surmise what the Buddha would have said about that!

The Buddha saw the limits of rationality and logic, at the very least in his understanding that language is limited in that it cannot describe the ineffable, possibly paralleling Tarski's undefinability theorem.. but I am biased! :p

Of the six methods of acquiring knowledge (https://en.wikipedia.org/wiki/Pramana), as seen within classical Indian philosophy, Buddhism embraces perception and inference. But in seeing the limits of inference ends up with the point made in the Kalama Sutta (as in another answer),

So in this case, Kalamas, don't go by reports, by legends, by traditions, by scripture, by logical conjecture, by inference, by analogies, by agreement through pondering views, by probability, or by the thought, 'This contemplative is our teacher.' When you know for yourselves that, 'These qualities are unskillful; these qualities are blameworthy; these qualities are criticized by the wise; these qualities, when adopted & carried out, lead to harm & to suffering'...

placing perception as the only method of laying down the burden.

  • When Nargarjuna said that "The nature of things is non-nature", that statement is both true and ineffable? I have difficulty assigning a value to this statement (using plurivalent logic in the article). What is your opinion? – Kyoma May 4 '17 at 15:24
  • Who is Nargarjuna? And is he even a theravadin Buddhist? – TheDBSGuy Nov 28 '18 at 11:21
  • @Kyoma - There is much misunderstanding on this issue. You need only use Aristotelian logic.I cannot explain this here but try bernardokastrup.com/2017/05/… – PeterJ Nov 29 '18 at 12:09
  • The Buddha would, I suspect, have fully endorsed the law of contradiction. He would not have endorsed the misuse of it we see all the time in non-Buddhist philosophy. – PeterJ Nov 29 '18 at 12:12
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On the one hand, there is logic which is a set of rules for making deductions, inductions, etc. Even in the West, there are various. For instance, (1) classical logic and (2) intuitionistic logic. I believe that they have different ways of dealing with the law of excluded middle. I used to study more philosophy of logic than logic itself, and there are great differences in that respect between formal and intuitionistic.

In Buddhism, when logic is applied, there is no "set of rules for making deductions" that is different from those of classical formal logic.

Ilya Grushevskiy gave an explanation of the law of identity and law of non-contradiction that makes you think that Indian logic is different from classical logic. However, Tibetans give another explanation. We say: X does not exist inherently. Therefore, X is not inherently one with X, but it is conventionally so. It is not inherently different from not-X, but it is conventionally so. And so forth.

In the same way, the first verse of Nagarjuna's Karika says "Neither from itself nor from another, Nor from both, Nor without a cause, Does anything whatever, anywhere arise." We explain: of course, a tree arise from another conventionally, since a sprout, or a seed, is not a tree. But since it is not inherently produced, it does not inherently arise from another. We call that "refuting the four extremes of production."

When you say "Indian Logic should be understood as being a different system of logic than modern classical logic[...]" it could refer, not to logic itself but to:

  • Dialectic, as for instance that of Nagarjuna. Western scholars tend to describe it as negative, but that is a category that is applied as well to that of Western philosophers (such as Kierkegaard, for instance)
  • A set of propositions.
  • Epistemology.

Indian and Indo-Tibetan epistemology mainly describes types of consciousnesses. Consciousness is qualified as an object-posessor since it knows its object, and so we speak of seven types (or more or less, depending on the text). For instance, a "wrong consciousness" that engages its object erroneously, an "inferential cognizer", etc. Consciousness is always described in relation to the causes of its arising (a sense power, an object, a immediately preceding condition) and is thus not taken independently. In the Indo-Tibetan traditions, one studies epistemology so as to know how mind works. It is all aimed at mind training and is not merely "philosophical" in that sense.

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    When you say "formal logic", I think you mean to "classical logic". Both classical logic and intuitionistic logic are formal logics, and there are many other formal logics with their own syntax and semantics (reasoning about time, duty, causality, etc.). You have a formal logic if you have a mathematically precise way to make statements (syntax) plus a way to determine if those statements are true or not (semantics). You have a deductive system if you have a mathematically precise way to make inferences about your logic. – Maarten Jan 3 '17 at 14:09
  • Gödel proved that human mathematical reasoning cannot be caught in traditional "complete and consistent" logics, because humans are not consistent in a mathematical sense (and I'd say we don't reason mathematically symbolical) giving rise to e.g. paraconsistent logics. – Maarten Jan 3 '17 at 14:11
  • To be more precise, Gödel proved that there are statements about natural numbers that are true, but there is no way to create a consistent formal system of axioms and algorithms to prove all these statements. So only if you assume that humans can prove all these statements to be true, the conclusion holds that human reasoning cannot be a consistent & complete system. I think that's obvious because our reasoning is inconsistent (we believe wrong things sometimes) and maybe incomplete (there may be things we may never know). – Maarten Jan 3 '17 at 14:27
  • @Maarten I changed "formal" to "classical", since it makes things clearer indeed. Thank you. As for "reasoning about time, duty, causality, etc" I wouldn't qualify that as logic itself (syntaxic, grammatical). It is propositions, expressions. – Tenzin Dorje Jan 4 '17 at 9:00
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    @Maarten = Gopel's incompleteness does not apply for the Buddhist world-view. This is because the latter denies the truth of all positive statements. This allows the non-dual world-view to transcend incompleteness - and all without any modification to Aristotle's rules. . – PeterJ Nov 29 '18 at 12:20
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Buddhist logic is to acknowledge that there is suffering.

Buddhist logic is to acknowledge that there are causes to these suffering.

Buddhist logic is to acknowledge that it is possible to be free from all suffering.

Buddhist logic is to acknowledge that there are paths that lead one to be free from all suffering.

  • This is the Four Noble Truths, not logic? – Kyoma Jan 7 '17 at 1:09
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The article shown by @llya Grushevskiy is discuss very interesting logic. Some extracts from it gives bellow.

... The four original possibilities, {T}, {F}, {T, F} and {}, as t, f, b and n, respectively....And now there is a fifth possible value – none of the above, ineffable, that which lies beyond language. Call it i, ....

We started with two possible values, T and F. In order to allow things to have both of these values, we simply took value of to be a relation, not a function. Now we have five possible values, t, f, b, n and i, and we assumed that value of was a function that took exactly one of these values. Why not make it a relation instead? That would allow it to relate something to any number of those five value.....In this construction, something can relate to both t and i: and so one can say something true about something ineffable after all.

The similarities between this and our Buddhist paradox of ineffability are, you must admit, pretty unnerving ....

i like to give example to 'i'.
Take "Life" as a fact.
So t = life is,
f = life is NOT,
b = life is AND life is NOT,
n = NOT life is OR NOT life is NOT,
then what should be the i?
i = 'life is' BUT 'a dream'.

....This does not, of course, show that they are true. That’s a different matter. But it does show that these ideas can be made as logically rigorous and coherent as ideas can be. As the Buddha may or may not have said (or both, or neither): ‘There are only two mistakes one can make along the road to truth: not going all the way, and not starting.

  • Nice point. If you check out George Spencer Brown's 'Laws of Form' he explains the logic of form and formlessness by way of a calculus and he uses 'i' to do it just as you suggest. He was a self-avowed buddha and friend of the advaitan teacher Wei Wu Wei. . . . – PeterJ Dec 7 '18 at 13:11
  • PS - Brown developed his logic to solve a problem in railway switching-systems. and then realised it solved metaphysics. It's an interesting story of how logical analysis can lead one to water even if it can't make us drink. – PeterJ Dec 7 '18 at 13:14
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In Aggi-Vacchagotta Sutta, it has mentioned Vacchagotta used Catuskoti to ask questions from Shakyamuni Gautama Lord Buddha. But Shakyamuni Gautama Lord Buddha has rejected all the conditions in Catuskoti.

"Any consciousness by which one describing the Tathagata would describe him: That the Tathagata has abandoned, its root destroyed, made like a palmyra stump, deprived of the conditions of development, not destined for future arising. Freed from the classification of consciousness, Vaccha, the Tathagata is deep, boundless, hard to fathom, like the sea. 'Reappears' doesn't apply. 'Does not reappear' doesn't apply. 'Both does & does not reappear' doesn't apply. 'Neither reappears nor does not reappear' doesn't apply."

This is because Dhamma (doctrine) is atakkavachara. In other words, Dhamma is beyond reasoning and logic.

  • "In other words, Dhamma is beyond reasoning and logic" - Well said. – Lanka Nov 28 '18 at 11:59
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I would say Buddhist logic is no different from Aristotle's. Nagarjuna uses Aristotelian logic in Fundamental Wisdom to refute all false views. This is often misunderstood for two reasons.

First, where he addresses positive metaphysical propositions he refutes not just the proposition and its contradictory alternative (this or that) but also their combination or separation (neither or both). This is sometimes seen as a novel form of logic but if we see this as two contradictory pairs of proposition then it is just the application of Aristotle's dialectic method.

Second, Nagarjuna denies that positive metaphysical statements form legitimate contradictory pairs of the form A/not-A. Thus when we ask 'Does the world begin with something or nothing' he would deny that this is a Aristotelian contradiction and this is why he is able to propose a third alternative without breaking Aristotle's rules.

Nagarjuna's logic would not work if he rejected Aristotle's rules. Buddhist logic does not reject them but transcends them. I would say that if you understand Aristotle's logic them you understand Buddhist logic.

Many people do not understand this issue because they forget Aristotle's definition for a true contradictory pair. For a legitimate case of A/not-A for which the 'laws of thought' would apply it must be the case that one of A and not-A is true and one false. Nagarjuna shows that metaphysical dilemmas and Kant's antinomies do not take this form and this is how he is able to refute both the extreme views that create these antinomies and endorse a third alternative. He does this without any need to modify Aristotle's rules.

This issue is much misunderstood because a surprising and dismaying number of philosophers do not properly apply Aristotle's rules in their own reasoning.

In short, it is my opinion that Buddhist logic is no different from the logic we use every minute of the day in our thinking. Were it to break the 'laws of thought' we would not be able to understand Buddhist doctrine.

As a consequence, and as Nagarjuna demonstrates (also Francis Bradley, Spencer Brown and others) it is possible to logically prove that all positive metaphysical positions are logically indefensible and in this way prove by the dialectical method and 'abduction' that Buddhist non-dual metaphysics is the only global theory that works.

For this reason the dialectic is big deal in Buddhist education.

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In the original Pali scriptures, it is taught to not rely on logic:

So in this case, Kalamas, don't go by reports, by legends, by traditions, by scripture, by logical conjecture, by inference, by analogies, by agreement through pondering views, by probability, or by the thought, 'This contemplative is our teacher.' When you know for yourselves that, 'These qualities are unskillful; these qualities are blameworthy; these qualities are criticized by the wise; these qualities, when adopted & carried out, lead to harm & to suffering'...

Kalama Sutta

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