Dignāga (born c. 480 ce—died c. 540) was a Buddhist logician and author of the Pramāṇasamuccaya (“Compendium of the Means of True Knowledge”), a work that laid the foundations of Buddhist logic. Dignāga gave a new definition of “perception”: knowledge that is free from all conceptual constructions, including name and class concepts. In effect he regarded only pure sensation as perception. In his theory of inference he distinguished between inference for oneself and inference for the other and laid down three criteria of a valid middle term (hetu)—i.e., that it should “cover” the minor premise (pakṣa), be present in the similar instances (sapakṣa), and be absent in dissimilar instances (vipakṣa). In his Hetucakra (“The Wheel of ‘Reason’”), Dignāga set up a matrix of nine types of middle terms, of which two yield valid conclusions, two contradictory, and the rest uncertain conclusions. Dignāga’s tradition was further developed in the 7th century by Dharmakīrti.