Inspired by various visions of the origin and order of the universe, these dozen or so early Greek thinkers, called “investigators of nature” by Aristotle and “Pre-Socratic philosophers” by later scholars, shared a passion for discovering the root nature of things. Modern knowledge of their ideas is based on fragments of their writings, and scholars recognize that this understanding has been colored by such philosophers as Aristotle, who first analyzed their doctrines.
Through religious myths, ancient Greeks tried to answer such questions as how the universe began, what its composition was, and what caused its order. Repudiating supernatural explanations, the Pre-Socratics answered these questions through natural rationales. The earliest Pre-Socratics came from Miletus in Ionia. These Milesian philosophers believed that the universe’s unity was grounded in the material of which it was made: For Thales of Miletus, it was water; for Anaximander, the “indefinite”; for Anaximenes, air; and for Heraclitus, fire. Thales’ theory that water is the origin of all things was most likely derived from myths. Anaximander, who was critical of Thales, felt that if water were the originative stuff, then such things as fire could not have come into existence. For Anaximander, the universe was made not of any definite element but of the indefinite. Anaximenes tried to convince his fellow Milesians that the basic stuff was air, which produced all other things through condensation and rarefaction, and he was unbothered by the objection that condensed air is still air. Heraclitus of Ephesus modified the Milesian approach by...
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