  Neither the canonical literature nor the early Abhidharma schools  provide detailed accounts of the means by which we may discriminate  between veridical and non-veridical states of cognitive awareness.  Works such as the Kathāvatthu (ca. 150 C.E.) do concern themselves with the rules and the various types of debate and  consider a wide range of views, but there is no systematic account of the criteria that ensure certainty. For systematic treatments of the  epistemological import of various states of cognitive awareness we  must turn to the Buddhist logico-epistemological tradition  (pramāṇavāda) initiated by Dignāga (ca. 480–540) and Dharmakīrti (ca. 600–660) [I will refer  to these two thinkers, and to their followers, as  ‘epistemologists’ so as to highlight that their concerns  are primarily epistemological]. It is generally agreed that this  tradition sprang out of a growing preoccupation with issues of logic  and language among those Buddhists who regarded polemical engagement  with their Brahmanical opponents as vital to their philosophical  enterprise (see Frauwallner 1959, Hattori 1968, Hayes 1988, Matilal  1998). In spearheading his model of epistemological inquiry  Dignāga (and following him, Dharmakīrti) significantly  changed the course of Buddhist philosophy in India. 