Arthāpatti does not depend on observation of pervasion or background belief. It is certain in the sense that when S cognizes P through postulation, no other epistemic instrument would invalidate P. The Naiyāyika tries to reduce postulation to anumāna and/or tarka. I shall argue that it is neither. Due to its explanatory role, one may think that postulation plays an essential role in lakṣaṇā or indication. But this too is a misconception. Both tarka and lakṣaṇā depend on observation and background (...) knowledge. Neither of them has the epistemic certainty postulation enjoys. I think, due to its observation-independent nature and certainty, postulation can be seen as the source of the knowledge of the truths of reason. (shrink)