The Buddhist Dharmottara in his commentary on _Nyayabindu_ says that people who are anxious to fulfil some purpose or end in which they are interested, value the knowledge which helps them to attain that purpose. It is because knowledge is thus found to be useful and sought by men that philosophy takes upon it the task of examining the nature of true knowledge (_samyagjnana_ or _prama@na_). The main test of true knowledge is that it helps us to attain our purpose. The Jains also are in general agreement with the above view of knowledge of the Buddhists [Footnote ref 283]. They alsosay that knowledge is not to be valued for its own sake. The validity (_prama@nya_) of anything consists in this, that it directly helps us to get what is good for us and to avoid what is bad for us. Knowledge alone has this capacity, for by it we can adapt ourselves to our environments and try to acquire what is good for us and avoid what is bad [Footnote ref 284]. The conditions that lead to the production of such knowledge (such as the presence of full light and proximity to the eye in the case of seeing an object by visual perception) have but little relevancy in this connection. For we are not concerned with how a cognition is produced, as it can be of no help to us in serving our purposes. It is enough for us to know that external objects under certain conditions assume such a special fitness (_yogyata_) that we can have knowledge of them. We have no guarantee that they generate knowledge in us, for we are only aware that under certain conditions we know a thing, whereas under other conditions we do not know it [Footnote ref 285]. The enquiry as to the nature of the special fitness of things which makes knowledge of them possible does not concern us. Those conditions which confer such a special fitness on things as to render them perceivable have but little to do with us; for our purposes which consist only in the acquirement of good and avoidance of evil, can only be served by knowledge and not by those conditions of external objects.
Knowledge reveals our own self as a knowing subject as well as the objects that are known by us. We have no reason to suppose (like the Buddhists) that all knowledge by perception of external objects is in the first instance indefinite and indeterminate, and that all our determinate notions of form, colour, size and other characteristics of the thing are not directly given in our perceptual experience, but are derived only by imagination (_utprek@sa_), and that therefore true perceptual knowledge only certifies the validity of the indefinite and indeterminate crude sense data (_nirvikalpa jnana_). Experience shows that true knowledge on the one hand reveals us as subjects or knowers, and on the other hand gives a correct sketch of the external objects in all the diversity of their characteristics. It is for this reason that knowledge is our immediate and most prominent means of serving our purposes.
Of course knowledge cannot directly and immediately bring to us the good we want, but since it faithfully communicates to us the nature of the objects around us, it renders our actions for the attainment of good and the avoidance of evil, possible; for if knowledge did not possess these functions, this would have been impossible. The validity of knowledge thus consists in this, that it is the most direct, immediate, and indispensable means for serving our purposes. So long as any knowledge is uncontradicted it should be held as true. False knowledge is that which represents things in relations in which they do not exist. When a rope in a badly lighted place gives rise to the illusion of a snake, the illusion consists in taking the rope to be a snake, i.e. perceiving a snake where it does not exist. Snakes exist and ropes also exist, there is no untruth in that [Footnote ref 286]. The error thus consists in this, that the snake is perceived where the rope exists. The perception of a snake under relations and environments in which it was not then existing is what is meant by error here. What was at first perceived as a snake was later on contradicted and thus found false. Falsehood therefore consists in the misrepresentation of objective facts in experience. True knowledge therefore is that which gives such a correct and faithful representation of its object as is never afterwards found to be contradicted. Thus knowledge when imparted directly in association with the organs in sense-perception is very clear, vivid, and distinct, and is called perceptional (_pratyak@sa_); when attained otherwise the knowledge is not so clear and vivid and is then called non-perceptional (_parok@sa_ [Footnote ref 287]).