Hetu

Hetu (हेतु) means “cause” or “reason.” In logic, it refers to the middle term or the ground of inference — the reason that connects the subject to the property being proved.

Overview

The hetu is the second member of the Nyaya five-membered syllogism and the most critical element in inference. In “The hill has fire because it has smoke,” smoke is the hetu. A valid hetu must satisfy three conditions (trairupya, formulated by the Buddhist logician Dignaga): it must be present in the paksha (subject), present in at least a sapaksha (similar case), and absent from all vipakshas (dissimilar cases).

Philosophical Context

Hetu theory is the backbone of Nyaya logic. The Nyayasutras list inference (anumana) among the four pramanas and analyze the conditions under which a reason establishes its conclusion. Different fallacies (hetvabhasa) arise when one or more of these conditions fails. The Buddhist logician Dharmakirti grounded the hetu in svabhavapratibandha (the intrinsic relation between hetu and sadhya), which operates either as tadatmya (identity) or tadutpatti (causal production).

Interpretations

The Bhatta Mimamsa school emphasizes svatah-pramanya (intrinsic validity of knowledge) and treats hetu as secondary to direct perception. The Buddhist tradition, especially Dignaga and Dharmakirti, develops a sophisticated theory of vyabhicharibhava (pervasiveness) to define the hetu. The Navya-Nyaya school of Mithila further refined the concept with technical terms like vyapty-avritti (the universal cover).

Verification Notes

• Nyayasutras 1.2.1–4 defines the hetu and its three conditions.
• Dharmakirti’s Pramanavarttika is the key Buddhist source.
• Audited against Wikipedia and Encyclopedia of Indian Philosophies (September 2026).