Epistemology is a science devoted to the discovery of the proper methods of acquiring and validating knowledge.
Since man is not omniscient or infallible, you have to discover what you can claim as knowledge and how to prove the validity of your conclusions. Does man acquire knowledge by a process of reason — or by sudden revelation from a supernatural power? Is reason a faculty that identifies and integrates the material provided by man’s senses — or is it fed by innate ideas, implanted in man’s mind before he was born? Is reason competent to perceive reality — or does man possess some other cognitive faculty which is superior to reason? Can man achieve certainty — or is he doomed to perpetual doubt? The extent of your self-confidence — and of your success — will be different, according to which set of answers you accept.
Man is neither infallible nor omniscient; if he were, a discipline such as epistemology — the theory of knowledge — would not be necessary nor possible: his knowledge would be automatic, unquestionable and total. But such is not man’s nature. Man is a being of volitional consciousness: beyond the level of percepts — a level inadequate to the cognitive requirements of his survival — man has to acquire knowledge by his own effort, which he may exercise or not, and by a process of reason, which he may apply correctly or not. Nature gives him no automatic guarantee of his mental efficacy; he is capable of error, of evasion, of psychological distortion. He needs a method of cognition, which he himself has to discover: he must discover how to use his rational faculty, how to validate his conclusions, how to distinguish truth from falsehood, how to set the criteria of what he may accept as knowledge. Two questions are involved in his every conclusion, conviction, decision, choice or claim: What do I know? — and: How do I know it?
It is the task of epistemology to provide the answer to the “How?” — which then enables the special sciences to provide the answers to the “What?”
In the history of philosophy — with some very rare exceptions — epistemological theories have consisted of attempts to escape one or the other of the two fundamental questions which cannot be escaped. Men have been taught either that knowledge is impossible (skepticism) or that it is available without effort (mysticism). These two positions appear to be antagonists, but are, in fact, two variants on the same theme, two sides of the same fraudulent coin: the attempt to escape the responsibility of rational cognition and the absolutism of reality — the attempt to assert the primacy of consciousness over existence.