Epistemology (/ɪˌpɪstəˈmɒlədʒi/; from Ancient Greek ἐπιστήμη (epistḗmē) 'knowledge', and -logy), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Epistemologists study the nature, origin, and scope of knowledge, epistemic justification, the rationality of belief, and various related issues. Debates in epistemology are generally clustered around four core areas: