EPISTEMOLOGY: The epistemological doctrine of the Charvaka school is that perception ( pratyaksa ) is the only means of valid knowledge. The validity even of inference is rejected.
Inference is said to be a mere leap in the dark. We proceed here from the known to the unknown and there is no certainty in this, though some inferences may turn out to be accidentally true. A general proposition may be true in perceived cases, but there is no guarantee that it will hold true even in unperceived cases. Deductive inference is vitiated by the fallacy of petitio principii. It is merely an argument in a circle since the conclusion is already contained in the major premise the validity of which is not proved. Inductive inference undertakes to prove the validity of the major premise of deductive inference. But induction too is uncertain because it proceeds unwarrantedly from the known to the unknown. In order to distinguish true induction from simple enumeration, it is pointed out that the former, unlike the latter, is based on a causal relationship which means invariable association or vyapti. Vyapti therefore is the nerve of all inference. But the Charvaka challenges this universal and invariable relationship of concomitance and regards it a mere guess-work. Perception does not prove this vyapti . Nor can it be proved by inference, for inference itself is said to presuppose its validity. Testimony too cannot prove it, for, firstly, testimony itself is not a valid means of knowledge and secondly, if testimony proves vyapti , inference would become dependent on testimony and then none would be able to infer anything by himself. Hence inference cannot be regarded as a valid source of knowledge. Induction is uncertain and deduction is argument in a circle. The logicians, therefore, find themselves stuck up in the mud of inference.
It is interesting here to note that Shunyavada Buddhism and Advaita Vedanta also have rejected the ultimate validity of inference. There has been a long controversy between Udayana, the logician and Shriharsa, the Vedantin regarding the validity of inference and Shiharsa has denounced all attempts to prove the validity of inference. But there is a radical difference between the Charvaka view on the one hand, and the Shunyavada and the Vedanta view on the other. The Charvaka accepts the validity of perception and thereby upholds the truth of the means of valid knowledge, though he rejects all other means of knowledge as invalid. But the Shunyavada and the Advaitin reject the ultimate validity of all means of knowledge as such including perception, though they insist on the empirical validity of all means of knowledge. The distinction between ultimate and empirical knowledge is unknown to the Charvaka. To accept the validity of perception and, at the same time and from the same standpoint, to reject the validity of inference is a thoughtless self-contradiction.
The crude Charvaka position has been vehemently criticized by all systems of Indian Philosophy all of which have maintained the validity of at least perception and inference. To refuse the validity of inference from the empirical standpoint is to refuse to think and discuss. All thoughts, all discussions, all doctrines, all affirmations and denials, all proofs and disproof are made possible by inference. The Charvaka view that perception is valid and inference is invalid is itself a result of inference. The Charvaka can understand others only through inference and make others understand him only through inference. Thoughts and ideas, not being material objects, cannot be perceived; they can only be inferred. Hence the self-refuted Charvaka position is called sheer nonsense and no system of philosophy. Perception itself which is regarded as valid by the Charvaka is often found untrue. We perceive the earth as flat but it is almost round. We perceive the earth as static but it is moving round the sun. We perceive the disc of the sun as of a small size, but it is much bigger than the size of the earth. Such’ perceptual knowledge is contradicted by inference. Moreover, pure perception in the sense of mere sensation cannot be regarded as a means of knowledge unless conception or thought has arranged into order and has given meaning and significance to the loose threads of sense-data. The Charvaka cannot support his views without giving reasons which presuppose the validity of inference.