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Asama Vyapti

Asama Vyapti is a philosophical term suggesting the relationship between two terms having unequal extensions. Vyapti or invariable concomitance of two terms is the logical necessity for the possibility of inference, according to the Nyaya School of philosophy. The two terms of vyapti are hetu and Sadhya; hetu serves as the logical ground for inferring Sadhya. The Nyaya concepts of hetu, Sadhya and vyapti come close to the western logical concepts of middle term, major term and the major premise respectively.

Vyapti signifies the invariable pervasion of hetu by the Sadhya term. That is, all instances of the presence of hetu are necessarily instances of the presence of Sadhya as well. As such, hetu is always vyapya (the pervaded term), whereas Sadhya is always vyapaka (one that pervades). It is always the presence of the pervaded term that provides the logical ground for inferring the presence of the vyapaka term.

In the classical Nyaya example of vyapti of smoke and fire, smoke is the pervaded term (vyapya) and fir the vyapaka term. Therefore, the presence of smoke leads to the inference of fire and not vice-versa. The impossibility of inferring smoke on the basis of fire is due to the fact that all case of fire are not necessarily cases of smoke as well. That is, the extensions of fire and smoke are unequal. The term whose extension is pervaded by or contained within the extension of the other term is called hetu or vyapya and it serves as the grounds for inferring the other term, called Sadhya or vyapaka. Such vyapti allows unidirectional inference only.

Thus, a vyapti which involves terms of unequal extensions is called asama vyapti or visama vyapti. It is also known as non-equipollent invariable concomitance. The other possible kind of vyapti is sama vyapti or equipollent invariable concomitance in which both the terms have an identical extension. Thus, in case of sama vyapti either of the terms can serve as hetu or inferring the other term.