An inference, in order to be a way of knowing, must not only be capable of yielding a conclusion which is actually true, but it must also effect some progress in knowledge. The inferer must know something new by drawing an inference. Of course, by ‘knowing something new’ is not meant objective novelty; that means, it is not required of an inference that to be a way of knowing an inference must have an object which was not known before; what is required is that through the process of inference, the inferer should gain some knowledge in the conclusion, in the sense that the conclusion was not known to him when he knew the premises.

We are to consider now whether on the Nyaya theory of inference such epistemic progress is possible. We have seen that an epistemic progress can be said to be made by an inference, if the knowledge of the premises does not presuppose or include the knowledge of the conclusion; or, in other words, what is known in the conclusion had not been known in the premises. Apparently it seems that the process of inference as analysed in the Nyaya theory of inference, does not leave any scope for epistemic progress. Let us explain why.

We have seen that it is possible to infer s on the basis of h only if h is related to s by the relation of vyapti (pervasion), and the inferer is aware of that relation. This is clear from the inclusion of the cognition II ( vyapti-jnana) in the set of causal conditions leading to the inferential cognition (anumiti). If we want to infer, say, fire (s) from smoke (h), smoke should be related to fire by the relation of pervasion, meaning that wherever smoke is found fire is to be found; and we should also have a cognition of that relation. Now this relation of vyapti is a universal relation holding between all the members of the class of smokes and the members of the class of fires such that each member of the class of smokes is accompanied by some member of the class of fires. Here the smoke which is the hetu (the inferential mark) is regarded as the subjunct (anuyogin) of the relation of vyapti, and the fire which is the sadhya (the inferable property) is the adjunct (pratiyogin) of that relation. So the hetu is that which is pervaded and the sadhya is that which pervades. Now, so far as the relation of vyapti is concerned, the hetu smoke and the sadhya fire are taken as the class of smoke (sakala-dhuma) and the class of fire (sakala vahni) respectively, though in an actual inference a particular instance of smoke and a particular instance of fire figure as the hetu and the sadhya respectively. It must be admitted that when the inferer ascertains the universal relation of vyapti holding between the members of two classes viz. smoke and fire, he is also aware of the particular instance of fire which is to be inferred, because a relation cannot be cognised without cognising the relata at the same time and that particular instance of fire belongs to the class of fires which is one of the relata. So it can be alleged that the conclusion is already known at the time of knowing the premises. The same objection, which has been raised against the syllogism like ‘All men are mortal, Socrates is a man, therefore Socrates is mortal’. seems to hold in this case also. So, how can there be epistemic progress in the Nyaya theory of inference?

In order to be clear about the problem as well as the solution as regards epistemic progress in inference on the Nyaya theory we are to consider first the way of ascertaining the relation of vyapti (pervasion).

According to the Nyaya thinkers, the universal relation of pervasion is ascertained by perception (pratyaksa), aided by some indirect argument (anukula tarka),13 which helps to remove any doubt concerning the invariability of the relation or to remove a mistaken certainty that there is no such invariable relation in the case under consideration.

Let us explain. Taking the inference of fire from smoke as an example, we shall explain how to ascertain that smoke is related to fire by the relation of pervasion. One forms a belief concerning the relation of vyapti (pervasion) holding between the hetu, i.e., the smoke, and the sadhya, i.e., the fire, when one perceives at least one case of concomitance between smoke and fire, without coming across any case of absence of concomitance between the two and without entertaining any belief to the contrary. If one has an apprehension as to the possibility of there being some cases of absence of concomitance such a belief acts as an inhibitor to the belief concerning the relation of vyapti between the two. But if there is no such belief to the contrary, one can form a belief regarding the relation of vyapti under consideration and on the basis of that belief one can draw an interference.

Now it may be questioned as to how it is possible to establish the universal relation of vyapti (pervasion) by observing only one particular instance of concomitance? That is, by observing only one case of concomitance of smoke and fire in, say, a kitchen, how can one form a belief that there is a relation of pervasion between all the members of the class of smokes and the members of the class of fires, such that wherever smoke is present, fire is also present. It may be mentioned here that it is not the case that every member of the class of smokes is pervaded by every member of the class of fires, but by some member or other. In symbols:

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