||Epistemology, in philosophy, as its Greek derivation makes clear, is the theory of knowledge. There are various (apparent) sources of knowledge. The various faculties by which we perceive the world (vision, hearing, touch, taste and smell) seem to furnish us with knowledge of how the world currently is. Memory seems to furnish us with knowledge of how the world was. And imagination seems to furnish us with knowledge of how the world might have been.
Two central concerns of epistemology are the nature of knowledgeâ€”what knowledge isâ€”and the extent of knowledgeâ€”how much, if anything, we know.
What is knowledge? One traditional answer is this: knowledge is true justified belief. I know that London is big because my belief that London is big is true and justified. Another requirement for knowing seems to be that one\'s belief was acquired by a method which was, in the context, reliable. My belief that London is big satisfies this requirement, for it was acquired by a method which was, in the context, reliable: I trusted what my geography teacher said.
Philosophers have often distinguished two forms of knowledge. I know a priori that two plus two is four, for one can know that two plus two is four independently of experience. In contrast I know a posteriori that London is big, for one cannot know that London is big independently of experience: one must listen to what an expert says on the topic, travel through London, or look at it from above.
How much, if anything, do we know? Not a lot, according to sceptics. Sceptics hold that one cannot attain knowledge in various areas. Limited versions of scepticism hold that one cannot attain knowledge of the minds of others, of the unobserved, or of the external world. Global scepticism is the doctrine that we know (almost) nothing.
The issue of what knowledge is is not independent of the question of how much, if anything, we know. If indubitability were a necessary condition for knowledge, if one could know that London is big only if one could not doubt that London is big, then we would know almost nothing. In particular, I would not know that London is big, for I can doubt that it is: perhaps my geography teacher was lying, or perhaps my entire life is a dream and London does not even exist.
Attempted rebuttals of scepticism, attempts to show that we do know what we think we know, have often been foundationalist. It has been held that there is a set of foundational beliefs, beliefs which justify all other beliefs which count as knowledge but which do not themselves require justification in order to count as knowledge. Perhaps the foundational beliefs are about the given, the supposed raw data of one\'s own experience, uncontaminated by theoretical interpretation or cognitive interpretation. This foundation justifies all other beliefs which count as knowledge, concerning, for example, the external world and other minds. Coherentists hold that foundationalism is mistaken. There are no foundational beliefs, and beliefs all hang together, mutually adjusted, in a single, coherent web. AJ
See also a priori and a posteriori; causal theories; certainty; empiricism; foundationalism and coherentism; given; idealism; illusion; imagination; induction; introspection; knowledge; memory; naive realism; other minds; perception; rationalism; representative theory of perception; scepticism.Further reading J. Dancy, An Introduction to Contemporary Epistemology; , K. Lehrer, Theory of Knowledge.