Hetvabhasa

Origin. Nyaya school, systematized in commentaries on the Nyaya Sutras. Hetvabhasa means "fallacious reasons" — a taxonomy of ways inference can fail.

Mechanism. Valid inference requires the reason (hetu) to have the right relationship to the conclusion. The taxonomy identifies specific ways this relationship can be defective: the reason may be unestablished, the connection may be uncertain, the reason may prove too much or contradict itself. By checking against the taxonomy, you can diagnose exactly how an inference fails rather than simply noting it feels wrong.

Procedure. Check any inference against five major fallacies: (1) Asiddha (unestablished) — the reason itself is not accepted. "The hill has fire because of its cold" fails if the hill is not cold. (2) Savyabhicara (deviating) — the reason is present where the conclusion is absent. "Sound is eternal because it is knowable" fails because pots are knowable but not eternal. (3) Satpratipaksha (contradicted) — an equally strong reason supports the opposite conclusion. "Sound is eternal because it is produced" contradicts "sound is non-eternal because it is produced." (4) Badhita (defeated) — the conclusion is refuted by stronger evidence. "Fire is cold because it is a substance" is defeated by direct perception. (5) Viruddha (opposed) — the reason actually establishes the opposite. "Sound is eternal because it is produced" — but produced things are non-eternal.

Applies to. Evaluating arguments. Debate preparation and response. Checking your own reasoning before committing. Teaching rigorous thinking.

Limitations. The taxonomy is designed for the five-membered inference form; other argument structures may require different checks. Identifying which fallacy applies can itself be contested. The method detects bad inferences but does not generate good ones.