Parmenides
Greek Presocratic philosopher (c. 515 – c. 450 BCE), born in Elea, a Greek colony in southern Italy, founder —or at least the most influential figure— of the Eleatic school, and, for many historians, the thinker who invented metaphysics as a rigorous discipline based exclusively on logical reasoning, against the earlier mythopoetic tradition. His only work, an epic poem in hexameters titled On Nature, of which only fragments quoted by later authors such as Simplicius survive, takes the form of a revelation: an unnamed goddess guides the narrator in a celestial chariot to the gates of Night and Day, and there sets out to him the 'way of truth', contrasted with the deceptive 'way of opinion' followed by double-headed mortals. The central argument, of unprecedented logical audacity, holds that 'what-is is, and what-is-not is not': we can only think and speak of that which is, never that which is not, because thinking nothing is impossible; from this he deduces, with purely rational rigour and never appealing to sensory evidence, that being must necessarily be one, ungenerated, imperishable, eternal, motionless, indivisible and homogeneous, often compared to a well-rounded sphere, radically contradicting the testimony of the senses, which show us a world of plurality, motion and change. This sharp division between reason, which grasps immutable truth, and the senses, which deceive us with misleading appearances, established one of the fundamental philosophical problems that all subsequent philosophy —from Plato, who devoted an entire dialogue to him, to Kant— would have to confront. His disciple Zeno of Elea defended his doctrine with the famous paradoxes of motion (Achilles and the tortoise, the arrow, the dichotomy), designed to prove by reductio ad absurdum that motion and plurality, as we perceive them, are logically impossible, thereby establishing Eleaticism as one of the most enduring intellectual challenges in the entire history of philosophy.