Epistemology, the theory of knowledge, has traditionally competed for the primary role in philosophical inquiry. Sometimes epistemology has won, and sometimes metapysics, depending on the methodological and substantiative presuppositions of the philosopher.
The epistemologist asks what we know. Some philosophers have begun with an account of the nature of reality and then appended a theory of knowledge to account for how we know that reality. Plato, for example, reached the metaphysical conclusion that abstract entities, or forms, such as triangularity or justice, are real and all else is mere appearance. He also held that the, real is knowable, and he inquired into how we might know this reality. Aristotle, on the contrary, held that individual substances, such as individual statues or animals, are real, and inquired as to how we might have knowledge, especially general knowledge, concerning these substances.
It is hardly surprising that Plato and Aristotle produced vastly different theories of knowledge when they conceived of the objects of knowledge in such different ways. Their common approach, starting with metaphysics, we might refer to as metaphysical epistemology.
Other philosophers, most notably Ren Descartes, turned tables on the metaphysical approach by insisting that we must first decide what we can know about what is real and must remain skeptical about what is real until we have discovered what we can know. It is refer as skeptical epistemology. However, there is also a problem with this approach. When one once enters the den of skepticism, an exit may be difficult to find. Seeking to discover what he knew by following the method of doubting all that he could, Descartes imagined a powerful demon bent on deceiving us and thus found demonic doubt. It remains controversial whether such doubt admits of relief by reason. It seems natural to begin with skepticism with the hope of discovering what we know and what we do not, but if we first pretend to total ignorance, we shall find no way to remove it. Moreover, we shall lack even the meager compensation of knowing that we ere ignorant, for that too is knowledge.
To indicate the information sense of the word 'know' as being the one in question is quite different from analyzing the kind of knowledge we have picked out. What is an analysis of knowledge An analysis is always relative to some objective. It does not make any sense simply to demand the analysis of goodness, knowledge, beauty, or truth, without some indication of what purpose such an analysis is supposed to achieve. To demand the analysis of knowledge without specifying further what you hope to accomplish with it is like demanding blueprints without saying what you hope to build.
Many philosophers have been interested in the task of analyzing the meaning of the word 'know' (A. J. Ayer 1955, 76).
Indeed, many would argue that there is no need for philosophical analysis once we have a satisfactory analysis of the meaning of the term 'know'. This restrictive conception of philosophical analysis is sustained by a dilemma: either a theory of knowledge is a theory about the meaning of the word 'know' and semantically related epistemic terms, or it is a theory about how people come to know what they do. The latter is not part of philosophy