Anaximenes

(c. 610 - c. 545 BCE)

Ancient Greek Natural philosopher from Miletos of the Milesian School.

Anaximenes in opposition to his teacher, Thales, held that aera apeiron (infinite air) was the arche (first thing) in the cosmos. He proposed a process of causation whereby each element was derived in turn from “air” through an eternal process of condensation (making heavy) and rarefaction (making light).

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Also see the Internet Encyclopedia of Philosophy entry on Anaximenes for a more detailed discussion.