Epistemology is the branch of philosophy concerned with knowledge. Epistemologists study the nature, origin, and scope of knowledge, epistemic justification, the rationality of belief, and various related issues. Debates in contemporary epistemology are generally clustered around four core areas:

• The philosophical analysis of the nature of knowledge and the conditions required for a belief to constitute knowledge, such as truth and justification;
• Potential sources of knowledge and justified belief, such as perception, reason, memory, and testimony
• The structure of a body of knowledge or justified belief, including whether all justified beliefs must be derived from justified foundational beliefs or whether justification requires only a coherent set of beliefs; and,
• Philosophical scepticism, which questions the possibility of knowledge, and related problems, such as whether scepticism poses a threat to our ordinary knowledge claims and whether it is possible to refute sceptical arguments.