The Republic by Plato Part 4 Page 57

thing clearly cannot act or be acted upon in the same part or in relation to the same thing at the same time, in contrary ways; and therefore whenever this contradiction occurs in things apparently the same, we know that they are really not the same, but different.

Good.

For example, I said, can the same thing be at rest and in motion at the same time in the same part?

Impossible.

Still, I said, let us have a more precise statement of terms, lest we should hereafter fall out by the way. Imagine the case of a man who is standing and also moving his hands and his head, and suppose a person to say that one and the same person is in motion and at rest at the same moment — to such a mode of speech we should object, and