On Nature

Parmenides of Elea composed his philosophy as a hexameter poem, On Nature, surviving in substantial fragments quoted mainly by Simplicius, describing a journey in which a goddess reveals the difference between the Way of Truth and the deceptive Way of Opinion followed by ordinary mortals. The Way of Truth argues, through what is often called the first sustained deductive argument in Western philosophy, that non-being cannot be thought or spoken of, so what is must be ungenerated, imperishable, whole, unchanging, and one, since coming-to-be, perishing, and plurality would all require non-being to exist. This conclusion, that the changing, plural world of experience is mere appearance, set the central problem later Presocratics tried to solve: how to reconcile reason's demands with the senses' evidence. Ancient tradition names Xenophanes as his teacher, though modern scholars mostly treat this as later doxographic construction rather than a documented relationship.