  Two older Indian philosophical traditions, the early Nyāya (grounded in Gautama Akṣapāda’s Nyāya-sūtra, c. 100 C.E., and dealing mainly with logic, epistemology, and the theory of debate) and the Vaiśeṣika (grounded in Kaṇāda’s Vaiśeṣika-sūtra, c. 100 B.C.E., dealing mainly with ontology), developed in parallel until, at some point in the 11th or 12th century, they merged to form a new school, called “Navya-Nyāya”, the new Nyāya or “new reason” school (Ganeri 2011). Despite its name, Navya-Nyāya incorporates and develops classical Vaiśeṣika metaphysics as well as classical Nyāya epistemology. The Navya-Nyāya authors also develop a precise technical language through the employment of which many traditional philosophical problems could be clarified and resolved.  Navya-Nyāya techniques proved to be so versatile that they were employed, not just by philosophers, but also in poetics, linguistics, legal theory, and other domains of medieval Indian thought. The foundational text of this school was Gaṅgeśa’s brilliant and innovative Jewel of Reflection on the Truth (Tattvacintāmaṇi). The school continued to develop for about four centuries, reaching its heights with the works of Raghunātha, Jagadīśa and Gadādhara (Ganeri 2014). The sophisticated use this school made of its technical vocabulary made it increasingly inaccessible, and so, in the 17th and 18th centuries, several manuals or compendia were written to explain in simplified language the basic tenets of the school. I will describe the philosophical principles of Navya-Nyāya based on a synopsis of the most successful of these, Annambhaṭṭa’s The Manual of Reason (Tarkasaṃgraha; henceforth TS), together with its auto-commentary, the Dīpikā (henceforth TSD), This text was nicknamed Bāla-gādādharī, a sort of ‘Beginners Guide to Gadādhara’. As well as presenting the Vaiśeṣika theory of categories (a mixture of physical theory, metaphysics and philosophy of psychology), and the epistemological, methodological, and logical techniques of the new Nyāya system, The Manual of Reason interjects fascinating discussions on a wide variety of topics of philosophical interest, making the text an enjoyable and informative introduction to later Indian analytical philosophy (trans. G. Bhattacharya 1983; for discussion of the text, see also Athalye 1930, Atreya 1948, C. Bhattacharya 1966, Foucher 1949, Shastri 1961).