A question arises regarding the sources of knowledge. If we analyze it empirically, we can immediately ascertain two prominent sources of knowledge namely direct perception (pratyaksha) and logical inference (anuman). Anuman has inextricable relationship with and is based on pratyaksha. For example, if we see smoke somewhere, we do a logical inference and conclude that there must be fire. This is based on our earlier pratyaksha. Even for mathematical constructs where no immediate pratyaksha is noticed, it is to be admitted that those constructs have their origin in pratyaksha without which the very conception thereof is rendered impossible. This gives a very important conclusion that anuman cannot negate pratyaksha. It can explain pratyaksha but can never negate pratyaksha in totality. Thus, a logical model which concludes the pratyaksha in totality to be non-existent is a self-destructing model wherein it destroys the very genesis of itself and thus becomes invalid.
However, there is a third source of knowledge too. That comes into question when neither anuman nor pratyaksha work. Is it related to God? Hold on. It is much more familiar. Let us take an example. X is grandfather of Z. Y is father of Z. X, Y and Z are ordinary Indian citizens and they follow usual Indian culture. Z never questioned the fatherhood of Y or the grand-fatherhood of X. He never insisted on DNA test of Y so as to logically and experientially (objectively) prove in a conclusive manner that Y indeed is his father. Now the situation is peculiar. X had died even before the birth of Z. However, he had known from his father, mother etc that X was his grandfather. And he believed so. However, in these days he had come across several scientific discourses which categorically assert that logic and pratyaksha are the sole sources of knowledge. That anything else is mere belief deserving little or no credence. That it is childish to conduct one’s life on the basis of belief. The assertion appeals to Z. However, Z is now caught in a peculiar problem. He has made a house and wants to name it after his grandfather. He is sure that he has a grandfather for there is no human being without a grandfather. But the problem is that he is unable to know as to who is his grandfather either experientially (by pratyaksha) or through logic. His grandfather is no more and he can neither conduct DNA test nor any other means can be utilized to conclusively ascertain the grand-fatherhood through pratyaksha or anuman. He thus concludes that he cannot know as to who his grandfather is and that ‘X is Z’s grandfather’ is a belief deserving little or no credence and to conduct his life on the basis of belief is childish. However, he is now in a fix because he has to name his house. Should he bury his wish under this scientific assertion or do something else. He has concluded that no matter what his father, mother, grandmother, relatives say, he cannot conduct his life on the basis of belief. But how to fix the fix which he has put himself in, that is the question.
This is the kind of situation where we put ourselves in if we go about harping that pratyaksha and anuman are the sole sources of knowledge. Z has missed a trick here. He has put all beliefs on same pedestal and concluded that life should not be led according to belief. He has disregarded the source of belief. It is no brainer, as we all know, that X indeed is Z’s grandfather but that can be held only if shabda, word, is accepted as a valid source of knowledge. Shabda per se is not a valid source but shabda from a reliable person is indeed a valid source. However, there is again a catch. What if the reliable person too is suffering from infirmities which are possible because of him being a human? Thus, it is concluded that shabda from a reliable apaurusheya entity has to be valid source of knowledge.
Indian Philosophy understood this and found the Vedas to be such a valid source of knowledge which deal with the matters similar to finding Z’s grandfather that is stuff beyond the realm of pratyaksha or anuman. Being from apaurusheya source (this requires separate discussion), they are pretty much valid source of knowledge.