The tetralemma
A logic tool with four possible answers, used to dismantle every fixed opinion—including the answers themselves.
The tetralemma (catuṣkoṭi, "four corners") is a distinctive tool of Buddhist reasoning. Western logic usually assumes two options: a statement is either true or false. The tetralemma lays out four corners for any claim. Take a proposition like "the world is eternal." The four corners are: (1) it is so; (2) it is not so; (3) it is both so and not so; and (4) it is neither so nor not so. Every conceivable position on the question is meant to fall into one of these four boxes.
Why build such a scheme? In the earliest texts, the Buddha sometimes met a question by refusing all four corners—setting the question itself aside as misframed or unanswerable, a trap that would only feed speculation rather than reduce suffering. Later, the Madhyamaka ("Middle Way") philosophers, above all Nāgārjuna, sharpened the device into a precision instrument. They would take each of the four corners in turn and show that it leads to contradiction, so that none of them can be asserted as the final truth.
The point is not to land on a fifth secret answer. It is to expose that our urge to pin reality down into a fixed position is itself the problem, because reality is "empty"—free of the fixed essences our either/or thinking assumes. The tetralemma is therefore less a way to win an argument than a way to dissolve the false certainties on both sides of one, clearing space for a more direct, un-clutching way of seeing.