Plato: The Republic

4. BOOK IV (continued)

And it has this particular quality because it has an object of a particular kind; and this is true of the other arts and sciences?

Yes.

Now, then, if I have made myself clear, you will understand my original meaning in what I said about relatives. My meaning was, that if one term of a relation is taken alone, the other is taken alone; if one term is qualified, the other is also qualified. I do not mean to say that relatives may not be disparate, or that the science of health is healthy, or of disease necessarily diseased, or that the sciences of good and evil are therefore good and evil; but only that, when the term science is no longer used absolutely, but has a qualified object which in this case is the nature of health and disease, it becomes defined, and is hence called not merely science, but the science of medicine.

I quite understand, and I think as you do.

Would you not say that thirst is one of these essentially relative terms, having clearly a relation--

Yes, thirst is relative to drink.

And a certain kind of thirst is relative to a certain kind of drink; but thirst taken alone is neither of much nor little, nor of good nor bad, nor of any particular kind of drink, but of drink only?

Certainly.

Then the soul of the thirsty one, in so far as he is thirsty, desires only drink; for this he yearns and tries to obtain it?

That is plain.

And if you suppose something which pulls a thirsty soul away from drink, that must be different from the thirsty principle which draws him like a beast to drink; for, as we were saying, the same thing cannot at the same time with the same part of itself act in contrary ways about the same.

Impossible.