Nyāya (Sanskrit:न्यायः, nyāya), literally meaning "justice", "rules", "method" or "judgment", is one of the six orthodox (Āstika) schools of Hindu philosophy that affirm the Vedas. Nyāyas most significant contributions to Indian philosophy were systematic development of the theory of logic, methodology, and its treatises on epistemology.
Nyāya schools epistemology accepts four out of six Pramanas as reliable means of gaining knowledge – Pratyakṣa (perception), Anumāṇa (inference), Upamāna (comparison and analogy) and Śabda (word, testimony of past or present reliable experts). In its metaphysics, Nyāya school is closer to the Vaisheshika school of Hinduism than others. It holds that human suffering results from mistakes/defects produced by activity under wrong knowledge (notions and ignorance). Moksha (liberation), it states, is gained through right knowledge. This premise led Nyāya to concern itself with epistemology, that is the reliable means to gain correct knowledge and to remove wrong notions. False knowledge is not merely ignorance to Naiyyayikas, it includes delusion. Correct knowledge is discovering and overcoming ones delusions, and understanding true nature of soul, self and reality.
Naiyyayika scholars approached philosophy as a form of direct realism, stating that anything that really exists is in principle humanly knowable. To them, correct knowledge and understanding is different from simple, reflexive cognition; it requires Anuvyavasaya (अनुव्यवसाय, cross-examination of cognition, reflective cognition of what one thinks one knows). An influential collection of texts on logic and reason is the Nyāya Sūtras, attributed to Aksapada Gautama, variously estimated to have been composed between 6th-century BCE and 2nd-century CE.
Nyāya school shares some of its methodology and human suffering foundations with Buddhism; however, a key difference between the two is that Buddhism believes that there is neither a soul nor self; Nyāya school like some other schools of Hinduism such as Dvaita and Viśiṣṭādvaita believes that there is a soul and self, with liberation (mokṣa) as a state of removal of ignorance, wrong knowledge, the gain of correct knowledge, and unimpeded continuation of self.