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NYAYA THEORY OF KNOWLEDGE
between two terms, from one of which we may infer the other, but not vice versa. Thus we may infer fire from smoke, but not smoke from fire. As distinguished from this, a vyāpti between two terms of equal extension is called samavyāpti or equipollent concomitance. Here the vyāpti holds between two terms which are co-extensive, so that we may infer either of them from the other. Thus there is a samavyāptı between cause and effect, substance and attribute. We may infer the cause from the effect, the substance from the attribute, or vice versa Thus whatever is produced is non-eternal, and whatever is non-eternal is produced.
It will appear from the above that visamavyāpti is a universal proposition, of which only the subject is distributed, 1.e. taken in its entire extension A samavyāptı, on the other hand, is a universal proposition which distributes both the subject and the predicate. They would thus correspond respectively to the universal affirmative and universal negative propositions in Western logic. It is to be noted however that there are some universal affirmative propositions wbich distribute both their subject and predicate Thus
whatever is produced is non-eternal,' 'men are rational animals' are cases of samavyāptı or universal affirmative propositions in which both the subject and the predicate are distributed.
For any inference the minimum condition is some kind of vyāptı between the middle and major terms. It does not matter whether the vyāpti is sama or visama, i.e. equipollent or non-equipollent. This satisfies the fundamental law of syllogistic inference that one of the premises must be universal. Now the vyāpti between the middle and major terms means generally a relation of coexistence (sāhacarya) between the two, e.g. wherever there is smoke there is fire. Every case of coexistence, however, is not a
1 Yatra dhūmastatrāgnirti sāhacaryanıyamo vyåpth, T8, p 45
