Epistemology primarily investigates the concepts of knowledge, belief, and justification.

At its core, epistemology seeks to understand what knowledge is and how it differs from mere belief or opinion. A commonly accepted starting point in Western philosophy, dating back to Plato, defines knowledge as 'justified true belief.' This tripartite analysis suggests that for someone to know something, three conditions must be met: the person must believe it, it must actually be true, and the person must have good reasons or evidence (justification) for believing it. Each of these components, however, presents its own set of philosophical challenges and debates. The concept of 'belief' is foundational, referring to a mental state where one assents to the truth of a proposition. 'Truth' itself is a complex philosophical concept, often understood as a correspondence between a statement and reality, though other theories exist. Finally, 'justification' is perhaps the most debated aspect, concerning the evidence, reasons, or processes that provide rational grounds for holding a belief, transforming it from a mere hunch into a candidate for knowledge. Epistemologists explore various theories of justification, such as foundationalism, coherentism, and reliabilism.