Logos (UK /ˈloʊɡɒs/, /ˈlɒɡɒs/, or US /ˈloʊɡoʊs/; Greek: λόγος, from λέγω lego "I say") is an important term in philosophy, psychology, rhetoric, and religion. Originally a word meaning "a ground", "a plea", "an opinion", "an expectation", "word", "speech", "account", "to reason"[1][2] it became a technical term in philosophy, beginning with Heraclitus (ca. 535–475 BC), who used the term for a principle of order and knowledge.[3]

Ancient philosophers used the term in different ways. The sophists used the term to mean discourse, and Aristotle applied the term to refer to "reasoned discourse"[4] or "the argument" in the field of rhetoric.[5] The Stoic philosophers identified the term with the divine animating principle pervading the Universe. Under Hellenistic Judaism, Philo (c. 20 BC – AD 50) adopted the term into Jewish philosophy.[6] The Gospel of John identifies the Logos, through which all things are made, as divine (theos),[7] and further identifies Jesus as the incarnate Logos. Although the term "Logos" is widely used in this Christian sense, in academic circles it often refers to the various ancient Greek uses, or to post-Christian uses within contemporary philosophy, Sufism, and the analytical psychology of Carl Jung.