Parmenides c. 515 BC – c. 460 BC

Parmenides of Elea was a Pre-Socratic Greek philosopher of the late sixth and early fifth centuries BC, the founder of the Eleatic school and one of the most influential thinkers of the Pre-Socratic period. His one philosophical work, On Nature, surviving in roughly 150 fragments, is a hexameter poem in two parts: the Way of Truth, arguing that what is must be eternal, indivisible, unchanging, and one, and the Way of Opinion, an account of the deceptive world of mortal sense. His arguments against the reality of change and plurality decisively shaped subsequent Greek philosophy, prompting the responses of Empedocles, Anaxagoras, the Atomists, and Plato. Plato devoted an entire late dialogue to him, and his influence on Western metaphysics has been profound.

Parmenides was born around 515 BC in Elea, a Greek colony in southern Italy. The ancient sources connect him with the Pythagorean Ameinias and with Xenophanes of Colophon, and credit him with drafting laws for his city. Whatever the biographical details, by the early fifth century he had become the central figure of the Eleatic school and the teacher of Zeno of Elea and Melissus of Samos.

His sole work is a hexameter poem conventionally titled On Nature, of which around 160 lines survive. After a visionary proem in which a goddess receives the young thinker, the poem divides into the Way of Truth, a deductive argument about what is, and the Way of Opinion, a cosmology of mortal belief. Plato's Parmenides and Aristotle's Physics and Metaphysics are the principal ancient sources for his thought.

Parmenides argued that what is must be ungenerated, indestructible, indivisible, and changeless, and that nothing can come from nothing — a thesis that forced subsequent Greek thinkers to explain appearance, plurality, and change without abandoning intelligible being. His influence on Plato's theory of Forms, on Aristotle's metaphysics, and on the entire Western tradition of ontology is difficult to overstate. He is thought to have died around 460 BC.