Presocratic School of Ancient Greek Philosophy Texts

"Presocratic" is a modern label for the Greek thinkers active in the 6th and 5th centuries BCE whose work predates or overlaps the lifetime of Socrates (c. 470–399 BCE). They were not a single school but a broad movement, centred in Ionia and southern Italy, applied retrospectively by later writers who measured early philosophy against the figure of Socrates.

These thinkers carried out a shift from mythological to naturalistic explanation. They looked for physical causes within the world itself rather than in the actions of anthropomorphic gods, and they understood the universe as a κόσμος, an ordered arrangement that is intelligible to inquiry. Their work ranged across what would later be separated into physics, astronomy, and the study of what is.

The earliest group, the Milesians, sought a single originating stuff, the ἀρχή, from which all things come: Thales of Miletus (fl. early 6th century BCE) proposed water, Anaximenes (fl. mid-6th century BCE) air, and Anaximander (c. 610–546 BCE) the ἄπειρον, the boundless. Their shared method was rational argument in place of inherited story. Xenophanes of Colophon (c. 570–475 BCE) attacked anthropomorphic pictures of the gods and gave naturalistic accounts of phenomena such as the rainbow. Heraclitus of Ephesus (c. 540–480 BCE) taught that all things are in flux and that a common λόγος, a rational measure, governs the process. Parmenides of Elea (c. 515–445 BCE) pressed the demand for consistency further, arguing by pure reasoning that what truly is must be ungenerated, imperishable, and unchanging, and that the reports of the senses deceive, a conclusion that set a problem every later thinker had to face.

Later Presocratics answered that challenge with pluralist systems that could account for change while respecting Parmenides' logical constraints, among them Empedocles, Anaxagoras, and the atomists Leucippus and Democritus. Protagoras (c. 490–420 BCE) turned the same independence toward human affairs, questioning the knowability of the gods and the standing of human perception. In the later 5th century the Sophists shifted attention from the nature of the cosmos to human society, rhetoric, and conduct, and the inquiry the Presocratics had opened was then taken up and transformed by Socrates, Plato, and Aristotle.