Logos (λόγος) — One of the richest and most polysemous terms in the Greek philosophical vocabulary, spanning “word,” “discourse,” “reason,” “ratio,” and “definition.” It derives from the verb legein, which originally meant “to gather,” “to collect,” and by extension “to say,” “to state”: at this root, to speak is to order and to articulate. Heraclitus of Ephesus is the first to give the term genuine philosophical weight: for him the logos is the common rational principle that governs becoming and the unity of opposites — the law according to which “all things flow” — even though human beings live as though each possessed a private understanding, deaf to this shared ground. The Stoics take up and broaden the notion: the logos becomes the immanent divine reason that orders the cosmos and in which every being participates, containing the seminal reasons of things (logos spermatikos); from it follow both Stoic physics and the ethics of “living according to reason.” In a logical-rhetorical sense, logos also denotes the argument or reasoning, distinct from mythos (tale, narrative) — an opposition that marks the birth of philosophy as discourse demanding justification. Philo of Alexandria already conceived it as a mediator between God and the world, and the Prologue of the Gospel of John — “in the beginning was the logos… and the logos became flesh” — turns the concept into a cornerstone of Christian theology, fusing Greek inheritance with revelation. The term is thus closely bound up with notions such as nous (intellect) and the Latin ratio.
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