Plato: The Republic

4. BOOK IV (continued)

Exactly so, he said.

There is no difficulty in understanding this.

None whatever.

But the question is not quite so easy when we proceed to ask whether these principles are three or one; whether, that is to say, we learn with one part of our nature, are angry with another, and with a third part desire the satisfaction of our natural appetites; or whether the whole soul comes into play in each sort of action-- to determine that is the difficulty.

Yes, he said; there lies the difficulty.

Then let us now try and determine whether they are the same or different.

How can we? he asked.

I replied as follows: The same 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 should rather say that one part of him is in motion while another is at rest.

Very true.