Tattvacintāmaṇi (The Jewel of Reflection on Reality)

The founding text of Navya-Nyāya, the 'new logic' of later Indian philosophy, written by Gaṅgeśa in Mithilā. It is organised around the four means of knowledge that Nyāya accepts, in four books: perception, inference, comparison (upamāna) and testimony (śabda). Against the Mīmāṃsā view that cognitions are valid by default, Gaṅgeśa argues that the truth of a cognition is established by something outside it, and he defines knowledge as a cognition that presents a thing as having a feature it really has. The book on inference became the most studied part. It tests and rejects a series of definitions of pervasion (vyāpti), the invariable relation that licenses an inference, before giving Gaṅgeśa's own, and it includes an inference for the existence of God as maker of the world. Throughout, Gaṅgeśa develops a precise technical vocabulary of qualifiers, relations and limiting properties (avacchedaka), which later Indian thinkers in many fields adopted for exact argument.

It created the exact technical language in which Indian philosophers argued for centuries, and its analyses of knowledge and inference invite close comparison with modern logic and epistemology.