Nyaya Logic and Inference: Paksha, Hetu, Sadhya, Vyapti, Hetvabhasa, Tarka
Inference and its parts
Nyaya inference is structured by paksha (subject), hetu (reason), and sadhya (conclusion-property), with vyapti as the invariable relation between hetu and sadhya. The five-membered prayoga is pratijna, hetu, udaharana, upanaya, and nigamana.
Rules and fallacies
- Vyapti must be universal and free from vyabhicara; co-presence alone is not enough.
- Hetvabhasa is a defective reason. The main types are savyabhicara (deviating), viruddha (contradictory), satpratipaksha (counterbalanced), asiddha (unproved), and badhita (contradicted).
- Tarka is suppositional reasoning that exposes absurd consequences; it supports inquiry but is not an independent pramana.
- A valid hetu must be present in the paksha, invariably related to the sadhya, and not defeated by a counter-reason.
Worked example
Thesis: 'The hill has fire.' Reason: 'Because it has smoke.' Paksha is the hill; hetu is smoke; sadhya is fire. Udaharana: 'Wherever there is smoke, there is fire, as in a kitchen.' Upanaya applies the relation to this hill; nigamana concludes, 'Therefore the hill has fire.' The reasoning depends on vyapti, not on the mere sight of smoke.
Traps
Do not reverse vyapti carelessly: smoke implies fire, but fire does not always imply smoke. Do not confuse savyabhicara with asiddha. Do not treat tarka as proof. Do not omit upanaya and nigamana when the five-membered form is asked.