 Gaṅgeśa, the “Great Professor” (mahôpādhyāya), lived in the fourteenth century in northeastern India. In Sanskrit, he wrote a philosophic masterpiece called the “Jewel” solidifying several centuries of advances in epistemology and logic within the classical school of “Logic,” Nyāya. By all counts, Gaṅgeśa is one of the major figures not only in Nyāya but in the whole long and complex history of classical philosophy. Gaṅgeśa is traditionally taken to inaugurate “New” Logic, Navya Nyāya. However, the distinction between “Old” and “New” Nyāya is problematic, since over the tradition’s almost two-thousand-year history there are both numerous developments and solid lines of continuity. At no time is there a decisive revolution, not with Gaṅgeśa, and also not with Udayana, the eleventh-century Naiyāyika whom Gaṅgeśa follows more closely than any other thinker and whom scholars sometimes identify as the originator of Navya Nyāya. However, Nyāya’s methods of investigation and argumentation on a wide range of topic, and against opponents’ views—Buddhists in the early years, others later—do indeed become increasingly refined, and Gaṅgeśa’s work can in several ways be counted pivotal.