 However, this suggestion does not solve the problem, for reasons laid out in detail by Dharmakīrti (c. 7th century ce). His extensive writing on epistemology in general and on reason and argument in particular formed a watershed in classical India philosophy. Besides his magnum opus, Pramāṇa-vārttika (Gloss on the means of epistemic cognition), one of whose four chapters is devoted to inference (svārtha-anumāna), comprising 340 verses and a commentary by him to it, and another devoted to argument (parārtha-anumāna), which comprises 285 verses, he wrote several smaller works, including Pramāṇa-viniścaya (Settling on what the epistemic means of cognition are), Nyāya-bindu (Drop of logic), Hetu-bindu (Drop of reason) and Vāda-nyāya (Logic of debate). As he makes abundantly clear in verses 13–25 and his commentary thereto of the chapter on inference (svārtha-anumāna) of his Pramāṇa-vārttika, the simple failure to perceive something which has H but which does not have S is no guarantee that whatever has H has S; after all, while one has never encountered something which has H and does not have S, what guarantee is there that something which has H and does not have S is not among the things which one has yet to encounter? Dharmakīrti’s answer was that the truth of the first premiss is guaranteed by either of two relations obtaining between properties: the causation relation (tadutpatti) and the identity relation (tādātmya). Unfortunately, as one might suspect, Dharmakīrti’s solution does not work. (See Gillon 1991; see Steinkellner 2015 for a dissenting view.)