Parmenides

Parmenides is Heraclitus's mirror image and his most powerful opponent. While Heraclitus said everything changes, Parmenides argued nothing does — and worse, nothing can. His reasoning, delivered in hexameter verse as a vision from a goddess, is the first piece of rigorous metaphysical argument in the Western tradition.

His move: to think of something is to think of something. You cannot think of nothing — nothing is not a thing. So change, which requires that something come from nothing or pass into nothing, is impossible. What is, is one, eternal, unchanging, indivisible. Our senses, which seem to show change, are lying.

This argument is bizarre. It is also nearly impossible to refute on its own terms. Plato's central ideas, Aristotle's metaphysics, and most of medieval philosophy are responses to Parmenides. He invented the discipline of metaphysics by making its problem inescapable.