While other disciplines seek to add to human knowledge, philosophy aspires to tell us what knowledge is. When we ask what we mean when we say we know something, or what justifies such a claim to knowledge, we are raising an epistemological question.
Philosophers are engaged in epistemology when they attempt to construct theories of the nature of knowledge.
Epistemological questions arise naturally when there is some doubt about a claim which a rational person is being asked to believe. Thus, traditional epistemology can be construed as a conversation between the "sceptic" who challeneges a knowledge claim, and the epistemologist who attempts to show that the claim in question has met the criteria for "knowledge". Such a claim, which is known. is then said to be "justified." Much Western espitemology has centered around rival theories of justification.
Epistemological questions include the following:
What distinguishes knowledge from mere belief? What can be known with certainty? How can we know if we have knowledge? What can we know by reasoning alone? What can we know by sensory experience?