Vyapti

Vyapti, in Indian logic, is the concept of invariable or universal concomitance between two terms, especially the relationship between the middle term (hetu) and the major term (paksha) in a logical inference (anumana). The word comes from Sanskrit and is often translated as pervasion or universality of connection.

In classical Nyaya logic, an inference is formulated with several components, including pratijna (the statement to be proved), hetu (the reason), udaharana (an example), and vyapti (the universal connection). Vyapti expresses that wherever the hetu is present, the paksha will be present as well, and typically that where the hetu is absent, the paksha is not guaranteed. This universal linkage is what makes the hetu a reliable indicator for the inference.

Vyapti is established through observation, experience, and authoritative testimony, and it underpins the strength of an inference. A strong vyapti means the hetu reliably signals the presence of the paksha across instances; a weak or contested vyapti makes the inference dubious. A classic illustration is the statement: wherever there is smoke, there is fire. Here, smoke is the hetu and fire is the paksha; the claimed vyapti is the universal concomitance between the two.

Beyond Nyaya, the notion of vyapti has influenced Buddhist and other Indian logics, where it is treated as a criterion for the validity of inferential reasoning. Contemporary discussions often examine the scope and limits of vyapti, including how to handle exceptions and domain-specific variability while preserving the rational basis for inference.