Tetralemma

The tetralemma is a figure that features prominently in the classical logic of India. It states that with reference to any a logical proposition X, there are four possibilities:

    X (affirmation)
    \neg X (negation)
    X \land \neg X (both) equiv.
    \neg (X \lor \neg X) (neither)

Catuskoti

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.