The Doctrine of Trirupa Hetu

Summary

The doctrine of trirūpa hetu, or the three characteristics of a valid reason, is a cornerstone of Buddhist logic. This article traces its formulation from Dignāga through Dharmakīrti and later scholastics. The three characteristics require that a reason (hetu) be present in the subject (pakṣa), present in similar instances (sapakṣa) and absent in dissimilar instances (vipakṣa). Dignāga is often credited with establishing this triad, but the author shows that earlier sources alluded to similar criteria and that Dharmakīrti refined the doctrine, adding conditions like neutrality and non‑contradiction. The article examines textual passages from the Nyāyapraveśa and Hetucakra as well as Tibetan commentaries to elucidate the doctrine’s development. It discusses debates among Buddhist logicians about whether the three characteristics are sufficient and how they relate to Nyāya notions of vyāpti (pervasion). The author argues that the trirūpa criteria aim to ensure that the relation between reason and predicate is both universal and exclusive, thereby preventing fallacies. The article also touches on the influence of this doctrine on later Tibetan and Chinese logic.