 Suppositional reasoning is what a philosopher is good at, drawing out of implications of opposed views and testing them against mutually accepted positions, according to, broadly speaking, criteria of coherence but also of simplicity. Here we come to the vital center of the life of a classical philosopher, which is reflected in honorific appellations and book titles, dozens of which use ‘tarka’ as in “Crest Jewel of Reasoning” (tarka-śiro-maṇi).