Illustrations: Numerous B/w Figures Description: Key questions in the history of Navya-nyaya (New Nyaya) remain unresolved: when did this school of logic begin, who was its founder, what distinguishes Navya-nyaya from Pracina-nyaya (Old Nyaya), and so on. This book attempts to answer these key questions in Part I. Part II provides a translation, analysis, and critical edition of the Lion and Tiger Definitions of Invariable Concomitance Chapter (Simha-vyaghra-laksana: LT Chapter) of the Tattva-cintamani-rahasya (TCR) of Mathuranatha (16th-17th c.). The hypothesis adopted by the author with regard to the first question is that Udayana, who lived in the 11th century, is the founder of Navya-nyaya. This hypothesis is closely linked to the hypothesis offered regarding the second question, which is that the feature that distinguishes Navya-nyaya from the earlier school is its description of concepts and the structure of the world in terms of relation. Early Navya-nyaya authors, who flourished between Udayana and Gangesa (14th c.), devised specific terminology, of which delimitor (avacchedaka) and describer (niËpaka) are the most important, in order to identify or specify relation. This book attempts to illustrate the function of these and other Navya-nyaya terms from the viewpoint of relation. The main sources upon which the author has based his conclusions are Udayana s Laksanavali and the chapters on invariable concomitance or pervasion (vyapti) of the Nyaya-siddhanta-dipa (NSD) of Sasadhara (13rd-14th c.), the Tattva-cintamaÆi (TC) of Gangesa, and the TCR. Of these Sanskrit texts no scholar has worked on the Invariable Concomitance Chapter (Vyapti-vada) of the NSD in detail or the LT Chapter of the TCR. The latter chapter follows in the TCR the Five Definitions of Invariable Concomitance Chapter (Vyapti-pancaka), which Ingalls edited, translated, and analyzed in his epoch-making book Materials for the Study of Navya-Nyaya Logic (1951). One major innovation of this book made in Part II is to explain the structure of Navya-nyaya analysis by employing 86 diagrams based on the dharma-dharmin (property and property-possessor) relation, which serve as a visual aid and help readers to more easily understand the complicated structure of its analysis. The diagrams are also helpful in ascertaining how the definitions of invariable concomitance apply to individual cases and how the entities are connected in the application of the definitions. Another major innovation is: almost every sub-section of the LT Chapter of the TCR contains Mathuranatha s clarification of part of the two definitions; but this clarification does not give the definition incorporating prior clarifications and insertions; this book provides such a definition accompanied by a diagram. In other words, Part II illustrates the structure of the whole definition at every process of the clarification, which (definition) is never presented as such in Mathuranatha s text.