Parmenides thought that everything that exists had always existed. This idea was not alien to the Greeks. They took it more or less for granted that everything that existed in the world was everlasting. Nothing can come out of nothing, thought Parmenides. And nothing that exists can become nothing. But Parmenides took the idea further. He thought that there was no such thing as actual change. Nothing could become anything other than it was. Parmenides realized, of course, that nature is in a constant state of flux.
