Epistemology (/áµ»ËpÉªstáµ»ËmÉlÉdÊi/; from Greek á¼ÏÎ¹ÏÏÎ®Î¼Î·, epistÄmÄ, meaning 'knowledge', and Î»ÏÎ³Î¿Ï, logos, meaning 'logical discourse') is the branch of philosophy concerned with the theory of knowledge. Epistemology studies the nature of knowledge, justification, and the rationality of belief.