Parmenides

Parmenides of Elea was a Pre-Socratic philosopher who argued, against all appearance, that reality is a single, unchanging, eternal whole. In his poem On Nature he distinguished between the Way of Truth — where reason reveals that only Being exists and change is illusion — and the Way of Opinion, which describes the deceptive world of the senses. His argument that "what is not" cannot exist had a profound impact on subsequent Greek philosophy.