The Positive Sciences of the Ancient Hindus c10.64

c10.64

*The Nyáya Ground of Inference—Vyápti* नियतसाहचर्य्य. —Inference, then, in the Nyáya, depends on the ascertainment, not of the causal relation, nor of the relation of genus to species, but of a natural relation, between two phenomena, of invariable and unconditional concomitance (उपाधिविधुरः स्वाभाविकः सम्बन्धः व्याप्तिः—Udyotakara and Váchaspati). Of the two phenomena so connected, one is called the Vyápya or Gamaka (the sign, mark, or indicator), and the other Vyápaka or Gamya (the thing signified, marked, or indicated). In the relation of fire and smoke, for example, smoke is the Vyápya or Gamaka (sign or mark); and fire, the Vyápaka or Gamya (the thing signified or marked). Now the relation of Vyápti between *A* and *B* may be either unequal or equipollent (विषमव्याप्ति or समव्याप्ति). When *A* is the sign of *B*, but *B* is not the sign of *A*, the Vyápti is one-sided or unequal, and here a Vyápti is said to exist between *A* and *B*, but not between *B* and *A*. For example, smoke is a sign of fire, but fire is not universally a sign of smoke. When, therefore, the relation of Vyápti is an unequal one, as between smoke and fire, it is expressed in the proposition—Wherever the Vyápya (sign or mark, *e.g.* smoke) exists, the Vyápaka (the thing signified or marked, *e.g.* fire) also exists. From this it follows by necessary implication (a sort of अर्थापत्ति) that whenever the Vyápaka (*e.g.* fire) is absent, the Vyápya (*e.g.* smoke) is also absent (व्यापकाभावे व्याप्याभावः). Again, the Vyápti may be a mutual or equipollent one, *i.e.* *A* and *B* may be signs of each other, *e.g.* green-wood fire and smoke. Here each in turn is Vyápya and Vyápaka, and this is expressed in the two propositions :—(1) Wherever there is smoke there is green-wood fire, and (2) wherever there is green-wood fire there is smoke. By necessary implication it follows—(1) Where there is no green-wood fire there is no smoke; (2) where there is no smoke there is no green-wood fire. We have seen that a Vyápti exists between smoke and fire, for wherever there is smoke there is fire, but we cannot say that a Vyápti exists between fire and smoke, for we cannot say that wherever there is a fire there is smoke. The combustion of an iron ball (अयगोलक), for example, is a case of fire without smoke. But it would be correct to say that a Vyápti exists between green-wood fire and smoke, as well as between smoke and green-wood fire. The question, therefore, is: what is the relation between fire and smoke? The relation between fire and smoke is a conditional relation; *i.e.* on condition that the fire is green-wood fire, it would be a sign of smoke. In other words, a Vyápti implies unconditional invariable concomitance, and the relation between fire and smoke is not therefore a Vyápti (natural unconditional concomitance), for fire requires a "condition," Upádhi, viz. green-wood, to be followed by smoke. Smoke, on the other hand, requires no "condition" to indicate fire. For the purposes of Inference, therefore, relations between phenomena may be considered as of two kinds: (1) Contingent conditional relations, holding good on the fulfilment of a certain condition or Upádhi, and (2) Vyápti, or unconditional invariable relation, between a mark and that which it marks, a relation without any Upádhi or determining condition (उपाधिविधुरः सम्बन्धः). It is this latter kind of relation that serves as the ground of inference. If we can ascertain that a Vyápti exists between *A* and *B*, then *A* is a sign of *B*, and an inference of the presence of *B* from the presence of *A*, and of the absence of *A* from the absence of *B*, would be warranted. The question, therefore, is, how to ascertain the relation of Vyápti between two phenomena.