What does jñāpaka mean? Literally it means ‘what causes to know’ and if you have been working on Sanskrit śāstra you will most probably immediately think of Sanskrit Grammar. Patañjali uses this term in this sense of “an indirect or implicitly revealing statement” (Freschi and Pontillo, section 2.7, p. 56) and analyses in this way Pāṇini’s Aṣṭādhyāyī. For instance, Patañjali might say that Pāṇini does not state X explicitely, but that he explicitly put a jñāpaka of X in the Aṣṭādhyāyī, so that one can conclude that X. A fuller definition of jñāpaka can be read in Abhyankar and Jośi’s Dictionary of Sanskrit Grammars. You can read some further example in Freschi and Pontillo, sections 18.104.22.168 and 22.214.171.124.
Now, “our” Aleix Ruiz-Falqués recently wrote me about the usage of the parallel ñāpaka in Pāli:
I found some discussion about ñāpakas in Pāli grammar. The point is that in one of the classifications, the grammarian posits three types of ñāpaka for the stock example of anumāna: a svabhāva ñāpaka is heat (which is in the nature of fire), a vyatireka ñāpaka is coldness (absence of heat implies absence of fire), and the third ñāpaka is the classical causative ñāpaka, smoke. As far as I know, mentioning “heat” as a cause for the inference of fire is not common in Sanskrit śāstra. […] Maybe I am wrong, but I think this business with the heat is a Buddhist insertion (because according to Abhidhamma the tejodhātu is always characterised by heat, so any heat will pressupose tejodhātu, the fire element).
To me, it seems that these texts use the examples of anvaya ‘concomitant presence’ and vyatireka ‘concomitant absence’ to explain the meaning of jñāpaka. svabhāvajñāpaka might be what Dharmakīrti and his school call svabhāvahetu in inference, although I do not know of uses of the example of heat and fire in this context.
What do you think? Have you ever encountered svabhāvajñāpakas? And fire as an instance of it?