Nyāya on Śabda: Reliability, Trustworthiness, and the Conditions of Valid Testimony

The Nyāya school, the "school of logic" founded by Gautama (c. 2nd century BCE) and systematized across centuries of commentary, is the most analytically rigorous of the classical Indian schools on questions of epistemology. Its Nyāya Sūtras define and analyze the four pramāṇas with a precision that rivals anything in contemporary analytic philosophy.

Nyāya defines śabda as: the assertion of a trustworthy person (āptavākya). A verbal statement generates valid knowledge when two conditions are met: (1) the speaker (āpta) genuinely knows the truth about the subject matter, and (2) the speaker communicates it accurately and sincerely. When these conditions fail, when the speaker is mistaken, or when they lie, the resulting cognition is invalid.

The āpta, the reliable testifier, is characterized as someone who has direct knowledge of the subject (through perception, inference, or their own reliable testimony), who is free from defects (perceptual errors, inferential mistakes, memory failures), and who has the intention to communicate truthfully without distortion by self-interest. This is a demanding standard, and Nyāya is clear that most testimony falls somewhere on a spectrum of reliability rather than being perfectly valid or completely invalid.

For Nyāya, both divine testimony (the Vedas) and human testimony (from reliable ordinary persons) count as valid śabda. The Vedas are considered the testimony of āptas, seers (ṛṣis) who had direct intuitive access to the truths they recorded. But crucially, the validity of Vedic testimony, for Nyāya, rests on the presumed reliability of those seers, it is not self-validating in the way Mīmāṃsā claims. This is a significant philosophical difference.

Nyāya also develops a sophisticated theory of linguistic understanding to explain how testimony works. A sentence does not produce knowledge simply by being heard. Understanding requires the hearer to grasp: (ākāṅkṣā) expectancy, the syntactic ways words await each other in a sentence. (yogyatā) compatibility, the semantic requirement that the words cohere ("water that fire" violates yogyatā). (āsatti/sannidhi) proximity, the words must be uttered in close enough sequence to function together. And (tātparya) intention, the hearer must correctly identify what the speaker intends to communicate. All four must be satisfied for testimony to generate valid cognition.

This theory anticipates several positions in contemporary philosophy of language. The condition of tātparya resembles Grice's distinction between sentence meaning and speaker meaning. The requirement of yogyatā anticipates semantic coherence conditions in formal semantics. And the overall framework of testimony analysis parallels reliabilist accounts (the validity of testimony depends on external facts about the speaker's reliability) in ways that illuminate both traditions.

According to Nyāya, a verbal statement is valid when it comes from a person who knows the truth and speaks the truth about anything for the guidance of other persons. Śabda as a pramāṇa is defined as valid verbal testimony, it consists in the assertion of a trustworthy person.

— WisdomLib, The Nyāya Theory of Knowledge, 'Part 1: The Nyāya Definition of Śabda'