A basic feature of Buddhist logic which distinguishes it from Western formal logic is that the Buddhist conception of what makes an argument good is grounded on the in-tuition that a good argument should start from true premises. In Buddhist logic, the truth of a premise is usually understood as being ascertained to be true by both the proponent and the opponent in a debate. Hence, the common ascertainment by both sides in de-bate, which is a special kind of epistemic condition, plays an essential role in defining the truth of a premise and in elucidating the standard of a good argument. Vocabularies used by Buddhist logicians to refer to this kind of epistemic condition, like siddha “established,” prasiddha “well established,” niścita “ascertained,” dṛṣṭa “observed” and vidita “known,” are considered by the present author as the epistemic operator in Bud-dhist logic. This paper is a preliminary study of the interpretation of this kind of epistemic operator by Buddhist logicians. In Nyāyamukha 2.2, Dignāga (c. 480–540 CE) claimed that not only the logical reason’s (hetu) being a property of the subject (pakṣa) but also the relation of the logical reason to the similar instances (sapakṣa) and to the dissimilar instances (vipakṣa) should be “ascertained by [both] the proponent and the opponent”(vādiprativādiniścita). By comparing the interpretation of this claim in the East Asian tradition of Buddhist logic, i.e., the hetuvidyā-tradition, with the interpreation of it by Dharmakīrti (c. 600–660 CE), this paper finds that the hetuvidyā-tradition held a dialectic interpretation of the epistemic operator in Buddhist logic. The “dialectic” inter-pretation means that an expression’s being “ascertained”/“[well] established”/“known” is simply to be equally accepted by both sides in debate on account of whatever evidence. In contrast, Dharmakīrti, in his Pramāṇavārttikasvavṛtti 13, 5–19, clearly refused this dialectic interpretation and proposed instead an epistemic interpretation of the epistemic operator. In this connection, he quoted and reinterpreted Dignāga’s above claim so as to support his epistemic interpretation. The “epistemic” interpretation means that an ex-pression’s being “ascertained”/“[well] established”/“known” is to be ascertained by both sides in debate only on account of certain epistemic evidences, namely, on account of certain means of valid cognition (pramāṇa).
