Parmenides was a pre-Socratic philosopher from the Greek colony of Elea in southern Italy, active in the early 5th century BCE. He is considered the founder of the Eleatic school of philosophy. According to ancient sources, he was of noble birth and may have written laws for his city. The details of his education are uncertain, with some accounts linking him to other thinkers like Xenophanes, but he stands as an original figure.
He is known for a single major work, a philosophical poem titled On Nature — ΠΕΡΙ ΦΥΣΕΩΣ runs the transmitted Greek heading — written in the epic metre of Homer. Only fragments of this poem survive, preserved through quotations by later ancient writers. In this work, Parmenides introduced a rigorous method of logical argument focused on what is. The poem's own words set ἀλήθεια, truth, against δόξα, the opinions of mortals, and describe what truly is as ἀγένητον, unborn. He argued that what is must be one, unchanging, indivisible, and eternal. According to his view, the everyday world of change and plurality is an illusion.
Parmenides's radical ideas set the problems for all later Greek philosophy. His monism posed a direct challenge to all later theories of the physical world. He profoundly influenced subsequent Greek philosophy, including the works of Plato and Aristotle, and the Eleatic tradition he founded remained a major intellectual force for generations.
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