  Certain topics concerning this account are addressed in The Manual of Reason and other Navya-Nyāya texts. Among them are: the conditions under which inference can take place, and the conditions under which the result is a knowledge-episode (TS 49, 54); the correct account of the inference-warranting relation, between the inferential sign and the property-to-be-inferred, called the ‘pervasion’ or ‘vyāpti’ relation (TS 50); the distinction between inference and demonstration (svārtha- and parārtha- inference) (TS 52, 53); the three-fold classification of inference types, those which are ‘universally positive’ (kevalānvayin), those which are ‘universally negative’ (kevala-vyatirekin), and those which are combined positive and negative (anvaya-vyatirekin) (TS 55); the types of inferential fallacy (hetvābhāsa) (TS 57-64).