• Cognition ( art of knowledge )
  • art of obtaining knowledge
  • art of using knowledge

• Methods and objects of inquiry
  • pramāna (valid means of knowledge or knowledge sources),
  • prameya (objects of valid knowledge),
• Conditions and the components of inquiry
  • samśaya (doubt),
  • prayojana (aim),
  • Dristant (example),
  • siddhānta (conclusion or accepted position),
  • avayava (members of syllogism or inferential components),
  • tarka (hypothetical/suppositional reasoning),
  • nirnaya (settlement or certainty),
• Forms of and strategies for debate
  • vāda (truth-directed debate),
  • jalpa (victory-directed debate),
  • vitandā (destructive debate),
  • hetvābhāsa (defective reasons),
  • chala (tricks),
  • jāti (sophisticated refutation or misleading/futile objections) and
  • nigrahasthāna (point of defeat or clinchers)

• The Naiyayikas (the Nyāya scholars) accepted four valid means (pramana) of obtaining valid knowledge (prameya) –
  • perception (pratyakṣa),
    • Main types
      • laukika (ordinary) ( external perception according to other scholars )
      • alaukika (extraordinary) ( internal perception according to other scholars )
    • There are four types of valid perceptions –
      • a) Indriya pratyaksha or sense perception,
        • indeterminate perception the chittashakti (intelligence-energy) acts as the substratum of the senses
      • b) Manas pratyaksha or mental perception,
        • chittashakti, with the aid of Buddhi, reflects upon objects of senses, and is a determinate perception
      • c) Svavedana pratyaksha or self-consciousness,
      • d) Yoga pratyaksha or super normal intuition
    • Pratyaksha knowledge gained through
      • Worldly pratyaksha
      • Transcendental pratyaksha
        • Samanya,
        • Lakshana,
        • Gyana lakshana
        • Yogaja
      • Pratyaksha (apparent or obvious) is divided into
        • Savikalpa,
        • Nirvikalpa
        • Pratibhigya.
    • modes or stages in perception
      • The first is called nirvikalpa (indeterminate), when one just perceives an object without being able to know its features.
      • second savikalpa (determinate), when one is able to clearly know an object.
      • third stage ( debated by scholars ) There is yet another stage called Pratyabhijñā, when one is able to re-recognise something on the basis of memory.
    • All laukika and alaukika pratyakshas are savikalpa, but it is necessarily preceded by an earlier stage when it is indeterminate.
  • inference (anumāna),
  • comparison and analogy (upamāna), and
  • word, testimony of past or present reliable experts or sources (śabda).

The Nyāya scholars, along with those from other schools of Hinduism, also developed a theory of error, to methodically establish means to identify errors and the process by which errors are made in human pursuit of knowledge. These include saṁśaya (समस्या, problems, inconsistencies, doubts) and viparyaya (विपर्यय, contrariness, errors)[35] which can be corrected or resolved by a systematic process of tarka (तर्क, reasoning, technique).

• Anumāna (inference)
  • types
    • inference for oneself (Svarthanumana, where one does not need any formal procedure, and at the most the last three of their 5 steps),
    • inference for others (Parathanumana, which requires a systematic methodology of 5 steps).
  • another classification
    • Purvavat (inferring an unperceived effect from a perceived cause),
    • Sheshavat (inferring an unperceived cause from a perceived effect)
    • Samanyatodrishta (when inference is not based on causation but on uniformity of co-existence).