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The Nyāya Sūtras are an ancient Indian text on of philosophy composed by Akṣapāda Gautama (also Gotama; c. 2nd century BCE). The sutras contain five chapters, each with two sections. The core of the text dates to roughly the 2nd century BCE, although there are significant later interpolations.
The Nyaya is sometimes called Tarka-Vidyā or the Science of Debate, Vāda-Vidyā or the Science of Discussion. Tarka is the special feature of the Nyāya. Thus some of its features and categories are better understood from that perspective. Gotama is sometimes given the honorific titles "Akṣapāda" (probably in the sense "having his eyes fixed in abstraction on his feet") and "Dīrghatapas" ("performing long penance"). He is also sometimes accorded the religious titles "Ṛṣi" or "Maharṣi".
In the Nyāya Sutras Gotama developed and extended the Vaiśeṣika epistemological and metaphysical system through 528 aphorisms. Later commentaries expanded, expounded, and critically discussed Gotama's work, the first being by Vātsyāyana (c.450–500 CE), followed by the Nyāyavārttika of Uddyotakāra (c. 6th–7th century), Vācaspati Miśra's Tātparyatīkā (9th century), Udayana's Tātparyapariśuddhi (10th century), and Jayanta's Nyāyamañjarī (10th century).
Purpose of the Nyaya Sutras 
"Gautama Ṛṣi, in his Nyāya Sūtras, proposes that one can attain liberation by negating both illusion and unhappiness: duhkha-janma-pravṛtti-dosa-mithyā-jnananam uttarottarapaye tad-anantarabhavad apavargah. "By successively dispelling false conceptions, bad character, entangling action, rebirth and misery -- the disappearance of one of these allowing the disappearance of the next -- one can achieve final liberation." (Nyāya Sūtra 1.1.2) But since Nyaya philosophers believe that awareness is not an essential quality of the soul, they teach that a liberated soul has no consciousness. The Nyāya idea of liberation thus puts the soul in the condition of a dead stone. This attempt by the Nyāya philosophers to kill the soul's innate consciousness is here called sato mrtim by the personified Vedas. But the Vedānta-sutra (2.3.17) unequivocally states, jno 'ta eva: "The jīva soul is always a knower." In the opening sūtra of the Nyāya Sūtra, it was claimed that the ultimate purpose of it is the attainment of liberation (niḥśreyasa), attained by knowledge of the sixteen categories (padārtha), which are:
- means of valid knowledge (pramāṇa);
- objects of valid knowledge (prameya);
- doubt (saṃśaya);
- purpose (prayojana);
- example (dṛṣṭānta);
- conclusion (siddhānta);
- the constituents of a syllogism (avayava);
- argumentation (tarka);
- ascertainment (nirṇaya);
- debate (vāda);
- disputations (jalpa);
- destructive criticism (vitaṇḍa);
- fallacy (hetvābhāsa);
- quibble (chala);
- refutations (jāti); and
- points of the opponent's defeat (nigrahasthāna).
Means of attaining valid knowledge 
According to the Nyaya Sutras, there are four means of attaining valid knowledge: perception, inference, comparison, and verbal testimony. The sutra ultimates implicitly develop a theory of causation. Cause and effect should be homogeneous in nature, and yet the effect is a new beginning and was not already contained in the cause.
The Buddhist thesis that all things are negative in nature (inasmuch as a thing's nature is constituted by its differences from others) is rejected, as is the view that all things are eternal or that all things are noneternal. Both these latter views are untrue to experience.
Thus, the resulting metaphysics admits two kinds of entities: eternal and noneternal. The whole is a new entity over and above the parts that constitute it. Also, the idea that God is the material cause of the universe is rejected. God is viewed as the efficient cause, and human deeds produce their results under the control and cooperation of God.
The five part syllogism 
The Nyaya Sutra supports a five-part syllogism, widely followed in the Indian tradition:
- This hill is fiery (pratijñā: a statement of that which is to be proved).
- Because it is smoky (hētu: statement of reason).
- Whatever is smoky is fiery, as is a kitchen (udāharaṇa: statement of a general rule supported by an example).
- So is this hill (upanaya: application of the rule of this case).
- Therefore this hill is fiery (nigamana: drawing the conclusion).
The characteristic feature of the Nyaya syllogism is its insistence on the example, which suggests that the Nyaya logician wanted to be assured not only of formal validity but also of material truth.
Types of logical error 
Five kinds of fallacious "middle" (hetu) are distinguished:
- the inconclusive (savyabhicara), which leads to more conclusions than one;
- the contradictory (viruddha), which opposes that which is to be established;
- the controversial (prakaranasama), which provokes the very question that it is meant to settle;
- the counterquestioned (sadhyasama), which itself is unproved; and
- the mistimed (kalatita), which is adduced "when the time in which it might hold good does not apply".
- Nandalal Sinha, Mahamahopadhyaya Satisa Chandra Vidyabhusana, The Nyaya Sutras of Gotama, The sacred books of the Hindus, 1930; Motilal Banarsidass, 1990 reprint, ISBN 978-81-208-0748-8; Munshiram Manoharlal reprint, 2003, ISBN 978-81-215-1096-7.
- Ganganatha Jha, Nyaya- Sutras of Gautama (4 vols.), Motilal Banarsidass, 1999 reprint, ISBN 978-81-208-1264-2.
Sources and reading 
- Sue Hamilton, Indian Philosophy: A Very Short Introduction (Oxford University Press, 2001) ISBN 0-19-285374-0
- B.K. Matilal, Epistemology, Logic, and Grammar in Indian Philosophical Analysis (Oxford University Press, 2005) ISBN 0-19-566658-5
- J.N. Mohanty, Classical Indian Philosophy (Rowman & Littlefield, 2000) ISBN 0-8476-8933-6
- B. K. Matilal "Perception. An Essay on Classical Indian Theories of Knowledge" (Oxford University Press, 1986), p. xiv.
- Encyclopædia Britannica (2007)
- All About Hinduism by Sri Swami Sivananda
- Chattopadhyaya, D. (1986). Indian Philosophy: A popular Introduction, New Delhi: People's Publishing House, ISBN 81-7007-023-6, p.163