The Greek term logos is multiply ambiguous. The unabridged Greek dictionary gives five and a half long columns of definitions and examples. Logos is a noun corresponding to the verb legein (say), signifying, among other things, speech, statement, sentence, account, definition, formula, calculation, ratio, explanation, reasoning, and faculty of reason. Early studies of the term tended to talk about a concept of logos, as if there were some single concept or theory associated with it. In fact, the term was employed in different ways by different thinkers. Yet, there is a kind of interplay in concepts associated with the term that makes a single study worthwhile.

Scholars sometimes speak of a change from mythos to logos; roughly, a transition in expression from storytelling in myths, usually expressed in poetry, to scientific, philosophical, or historical accounts, usually expressed in prose. Philosophers of the sixth century BCE were among the...