Introduction

Classical Indian pramāṇa theory includes not only what Western philosophers would count as epistemology, but also much that they would count as logic and philosophy of language. This is because almost all Indian philosophers recognized inference (anumāna) as an independent source of knowledge, and many recognized testimony (śabda) as a special kind of word-generated knowledge. This chapter focuses on Indian ‘logic’ (broadly conceived), and the next chapter addresses Indian debates about selected issues in the philosophy of language.

The history of Indian logic can be roughly divided into three periods (Vidyabhusana 1978): the ancient period (650 bce–100 ce), dominated by the Nyāyasūtra and its commentaries; the medieval period (up to 1200 ce), dominated by the Buddhist logicians Dignāga and Dharmakīrti; and the modern period (from 900 ce), dominated by Gaṅgeśa and the school of Navya-Nyāya, or ‘New Logic’.

Since the origins of Indian logic were in the ancient traditions of public debate, there were accordingly two distinct, though intertwined, parts to its development. One part (on which there is a very large literature) is to do with the search for a satisfactory model of inference and the consequent emergence of a formalized canonical inference schema. The other part is more to do with dialectics, and includes a concern with the nature of fallacies (hetvābhāsa). Both parts are evident in Gautama's Nyāyasūtra (second century), the foundational text for the development of ancient Indian logic.

Early Nyāya logic

In what became the most influential part of the Nyāyasūtra, Gautama identifies and systematizes a form of inferential argument used in debate. He defines an inference as having five members: the hypothesis (pratijñā); the ground or reason (hetu); the corroboration (dṛṣṭanta); the application (upanaya); and the conclusion (nigamana).

This account of inference may be seen as a regimentation of a conversation that might occur if two people were standing together looking at a mountain side from which they could see smoke rising. One of the persons involved remarks that there is a fire on the mountain. When asked for his reasoning he replies that he holds that there is a fire on the mountain side because there is smoke. He then appeals to familiar conjunctions of fire and smoke: as in a kitchen. Furthermore, he reminds his friend that one never sees smoke where there is no fire: as, for example, in a lake.