Anaximena

Anaximena was an ancient Greek philosopher and a student of Anaximander, both associated with the Milesian school of philosophy. He is believed to have lived in Miletus around the 6th century BCE. Anaximena's primary contribution to philosophy was his identification of air as the arche, the fundamental principle or substance from which all things originate and to which they return.

He proposed that the diversification of matter occurred through processes of rarefaction and condensation of air. Rarefaction, or thinning, of air was believed to produce fire, while condensation, or thickening, led to wind, clouds, water, earth, and finally stone. This concept represented a shift from his teacher Anaximander's more abstract apeiron. Anaximena's theory was more concrete and observable, suggesting a tangible substance as the source of all existence. His ideas laid groundwork for subsequent cosmological inquiries and demonstrated a developing understanding of natural processes.