Vyapti

Vyapti, a Sanskrit expression, in Hindu philosophy refers to the state of pervasion. It is considered as the logical ground of inference which is one of the means to knowledge. No conclusion can be inferred without the knowledge of vyapti. Vyapti guarantees the truth of conclusion. It signifies the relation of invariable concomitance between "hetu" and "sadhya" and is of two kinds. Vyapti between terms of unequal extension is called "asamavyavyapti" or "visamavyapti", and vyapti between equal extensions is called "samavyapti".

Vyapti is a universal statement that expresses the "niyata sahacharya" or relation of constant concomitance between hetu or the middle term and sadhya or the major term and implies the "sahacara" i.e. the knowledge of invariable relation of causality or co-existence between sadhya and hetu in all the three instances of time, which is possible when the "anupadhik sambandha" i.e. relation of unconditionality between the two is known. It is defined as the unconditional and constant concomitant relation between "vyapya", the pervaded, and "vyapaka", the pervader.

The Charvaka school of Hindu philosophy while admitting the existence of the world and denying pre-existence rejects inference and testimony; they recognize perception as the only means to knowledge. They hold the view that the universal concomitance of the middle term with the major term can never be known since their agreement in presence and agreement in absence can never be known as also their invariable concomitance because there are no class-characters and universals. Vyapti can never be known because it does not exist. If inductive inference is proved by vyapti then these two cannot be mutually dependent.

The Nyaya school of Gautama speaks of five-membered inference or "pararthanumana". Knowledge of vyapti is considered by this school to be the cause of successful inference because inference depends upon the unconditional universal concomitance between the middle term and the major term, the middle term indicating the existence of the major term, and is to be found in the minor term or "paksa", the subject of inference. It is not possible to perceive all instances of the middle term and the major term nor can vyapti be known by internal perception. In order for the inference to be sound the major and the minor premises have to be true, the former should be secure because the latter’s truth is given by perception. They hold the view that vyapti is the unconditional uniform relation of the reason to the predicate and that a condition pervades the predicate. Faulty reasons such as inconclusive ("savyabhicara"), contradictory ("viruddha"), counterbalanced ("prakaranasama"), unproved ("sadhyasama"), and mistimed ("atitkala") or contradicted ("badhita') hinder the production of a valid inference when they are known. Vyapti is known by the joint method of agreement in presence and agreement in absence based on repeated observation aided by favourable hypothetical reasoning. Doubt about vyapti and certainty of the absence of vyapti act as hindrances to inferential knowledge; the certainty about vyapti is the cause of inferential knowledge.

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