Parmenides of Elea

Parmenides of Elea (Greek: Παρμενίδης ὁ Ἐλεάτης; fl. early 5th century BCE) was an ancient Greek philosopher born in Elea, a Greek city on the southern coast of Italy. He was the founder of the Eleatic school of philosophy. The single known work of Parmenides is a poem which has survived only in fragmentary form. In this poem, Parmenides describes two views of reality. In The Way of Truth (a part of the poem), he explains how reality is one, change is impossible, and existence is timeless, uniform, and unchanging. In The Way of Opinion, he explains the world of appearances, which is false and deceitful. These thoughts strongly influenced Plato, and through him, the whole of Western philosophy.

Thinking and the thought that it is are the same; for you will not find thought apart from what is, in relation to which it is uttered. (B 8.34-36)

For thought and being are the same. (B 3)

It is necessary to speak and to think what is; for being is, but nothing is not. (B 6.1-2)

Helplessness guides the wandering thought in their breasts; they are carried along deaf and blind alike, dazed, beasts without judgment, convinced that to be and not to be are the same and not the same, and that the road of all things is a backward-turning one. (B 6.5-9)