Among the sixteen topics listed in the first sentence of the Nyāya Sūtras are the quibble, the futile rejoinder and the point at which a debater can be declared beaten. The list belongs to a world that settled its deepest questions in public argument, where Brahmin schools and Buddhists disputed what can be known and how. Yet the same sentence promises that correct knowledge of these sixteen things leads to the highest good. That pairing is the founding claim of Nyāya, the Indian school of logic and argument whose root text this is: learning to think correctly is itself the way out of suffering.
The text is ascribed to Akṣapāda Gautama, and beyond the ascription almost nothing about him is known. Nobody knows when he lived. Estimates for the sūtras run from the sixth century BCE to the second century CE; the Internet Encyclopedia of Philosophy places them around 200 CE, and the years on this page stand for that estimate, not for a recorded life. Many scholars think the five books grew in layers, by more than one hand. The tradition places Gautama at Mithilā, in what is now northern Bihar. It also explains his name Akṣapāda, "eye-footed", with a story: lost in thought about logic, he fell into a well, and God gave him a second pair of eyes in his feet to watch the road.
The sūtras count four means of knowledge — perception, inference, comparison and the word of a reliable person — and hold that through them we reach a world that is really there. A complete proof, in their account, runs in five steps: the claim, the reason, an example, the application of the example to the case, and the conclusion. The second sūtra says why this matters, tracing suffering back along a chain. Suffering comes from birth, birth from activity, activity from faults of character, and the faults from false knowledge. Remove false knowledge and the chain comes apart link by link, ending in release, apavarga.
The sūtras are terse, and readers have always met them through a teacher. The oldest commentary to survive is the Nyāya-bhāṣya of Vātsyāyana, written around the fifth century, and the text we hold is mostly his. It was Vātsyāyana, not Gautama, who claimed for the inquiry the place of ānvīkṣikī, "investigation", one of the four sciences named in the old Indian manual of statecraft. When Dignāga, a Buddhist logician, attacked Vātsyāyana's reasoning, Uddyotakara wrote a further commentary to defend it, and Vācaspati Miśra later commented on Uddyotakara in turn. Each generation of the school wrote on the layer beneath it. In the fourteenth century Gaṅgeśa Upādhyāya opened the school's "new" phase, navya-nyāya, and the methods of analysis that began in these sūtras came to shape Indian literary criticism, philosophical debate and law.
The sūtras' sharpest pages answer a skeptic. A means of knowledge, he argues, can be established neither before its object, nor after it, nor at the same moment, and so none can be established at all. The sūtras reply that his denial is itself a claim to know and falls to the same argument; someone who rejects every means of knowledge has nothing left to deny with. Nāgārjuna, the second-century Buddhist philosopher, turns the same three-way argument against the logicians, and scholars still debate which of the two texts is answering the other.