From Arche to Logos: The Birth of Rational Cosmology

Aristotle, writing in Metaphysics Book I roughly two centuries after the Milesians, gives us the very term through which their cosmology has since been organized: arche (ἀρχή), "beginning," "origin," or "ruling principle." He identifies Thales as the first to propose that a single material arche — water — underlies all the apparent change and diversity of nature (Metaphysics 983b), a move that presupposes the manifold, changing phenomena of the world can be reduced to, or derived from, one underlying principle or substance. Aristotle analyzes this arche as a material cause (hyle), distinguishing it from the formal, efficient, and final causes of his own four-cause framework — a scheme he applies retrospectively, and to some degree anachronistically, to thinkers who did not themselves draw these distinctions. The three Milesian candidates for arche — Thales's water, Anaximander's apeiron, and Anaximenes's air — share a double role: each is simultaneously the originating substance in a cosmogonic sense and the persisting substrate of all things in an ontological sense, a synthesis that Simplicius, in his 6th-century-CE Commentary on Aristotle's Physics, preserves for us by drawing on Theophrastus's own lost Physical Opinions.