The tetralemma is a figure that features prominently in the logic of India. It states that with reference to any a logical proposition X, there are four possibilities:
see De Morgan's laws.
The history of fourfold negation, the Catuskoti (Sanskrit), is evident in the logico-epistemological tradition of India, given the categorical nomenclature Indian logic in Western discourse. Subsumed within the auspice of Indian logic, 'Buddhist logic' has been particularly focused in its employment of the fourfold negation, as evidenced by the traditions of Nagarjuna and the Madhyamaka, particularly the school of Madhyamaka given the retroactive nomenclature of Prasangika by the Tibetan Buddhist logico-epistemological tradition.
A variant of the tetralemma is used in the Ancient Greek philosophical schools of Democritus and Pyrrhonism. Pyrrho includes it in his summary of his teachings, and Sextus Empiricus includes it among the Pyrrhonist Maxims.
- Sextus Empiricus, Outlines of Pyrrhonism Book 1, Section 19