Turning to more abstract and universal matters, the philosopher Parmenides of Elea (in southern Italy) tackled the perplexing issue of permanence versus change in the world. He convinced himself that everything in the universe must be eternal and unchangeable. Change requires motion, he reasoned, and motion requires empty space. But empty space equals nonexistence, which by definition does not exist.
According to the passage, Parmenides' theory that things do not move or change is grounded upon his assumption that: