Hetuchakra

The Hetucakra ("The Wheel of 'Reason'") is a work by Dignāga, a Buddhist logician active around the 5th-6th century CE. This text is part of his larger work, the Pramāṇasamuccaya, which established the foundations of Buddhist logic.12

In the Hetucakra, Dignāga presented a matrix of nine types of middle terms (hetu). These terms are crucial for valid inference, and Dignāga outlined three criteria for a middle term: it must "cover" the minor premise, be present in similar instances, and absent in dissimilar instances. His matrix categorized these middle terms, with two yielding valid conclusions, two leading to contradictory ones, and the rest resulting in uncertain conclusions. Dignāga's work significantly influenced the development of Buddhist logic and epistemology.12