-515 – -450
Parmenides of Elea (fl. c. 475 BCE) was a pre-Socratic Greek philosopher and founder of the Eleatic school of thought. He argued in his didactic poem 'On Nature' that reality is a single, unchanging, eternal whole, and that plurality and change are illusory appearances. His radical monism and insistence that 'what is, is' profoundly shaped subsequent Greek philosophy, particularly through Plato and Aristotle's engagements with his arguments.
Founded the Eleatic school of philosophy, establishing the first systematic metaphysical monism
Introduced the distinction between the 'Way of Truth' (rational being) and the 'Way of Appearance' (sensory illusion)
Argued that existence is one, eternal, motionless, and indivisible — the first sustained argument from pure reason in Western philosophy
Pioneered the use of logical deduction over empirical observation in metaphysics
Deeply influenced Plato's theory of Forms and Aristotle's analysis of being and change