Parmenides c. 515 bc?

Unlike Heraclitus who thought that everything changes, Parmenides though that nothing changed. He thought that the world that we perceived with our senses was an illusion and that the only true thing was 'the One', which was infinite and indivisible. This is another of the threads later picked up by Plato. For Parmenides 'the One' was not the union of opposites, as Heraclitus thought, since he thought that there were no opposites, cold being merely 'not hot', for example.

His ideas about knowledge and truth led him to think that change was an illusion. Russell summarises his ideas thus:

"When you think, you think of something; when you use a name, it must be the name of something. Therefore both thought and language require objects outside themselves. And since you can think of a thing or speak of it at one time as well as another, whatever can be thought of or spoken of must exist at all times. Consequently there can be no change, since change consists in things coming into being or ceasing to be."