Theaetetus

SO.What shall we do with all these people, my friend? For, advancing little by little, we have unwittingly fallen between the two parties, and, unless we protect ourselves and escape somehow, we shall pay the penalty, like those in the palaestra, who in playing on the line are caught by both sides and dragged in opposite directions. I think, then, we had better examine first the one party, those whom we originally set out to join, the flowing ones, and if we find their arguments sound, we will help them to pull us over, trying thus to escape the others; but if we find that the partisans of the whole seem to have truer doctrines, we will take refuge with them from those who would move what is motionless. But if we find that neither party has anything reasonable to say, we shall be ridiculous if we think that we, who are of no account, can say anything worth while after having rejected the doctrines of very ancient and very wise men. Therefore, Theodorus, see whether it is desirable to go forward into so great a danger.

THEO. Oh, it would be unendurable, Socrates, not to examine thoroughly the doctrines of both parties.

SOC. Then they must be examined, since you are so urgent. Now I think the starting-point of our examination of the doctrine of motion is this: Exactly what do they mean, after all, when they say that all things are in motion? What I wish to ask is this: Do they mean to say that there is only one kind of motion or, as I believe, two? But it must not be my belief alone; you must share it also, that if anything happens to us we may suffer it in common. Tell me, do you call it motion when a thing changes its place or turns round in the same place?

THEO. Yes.

SOC. Let this, then, be one kind of motion. Now when a thing remains in the same place, but grows old, or becomes black instead of white, or hard instead of soft, or undergoes any other kind of alteration, is it not proper to say that this is another kind of motion?

THEO. I think so.

SOC. Nay, it must be true. So I say that there are these two kinds of motion: alteration, and motion in space.

THEO. And you are right.

SOC. Now that we have made this distinction, let us at once converse with those who say that all things are in motion, and let us ask them, Do you mean that everything moves in both ways, moving in space and undergoing alteration, or one thing in both ways and another in one of the two ways only?

THEO. By Zeus, I cannot tell! But I think they would say that everything moves in both ways.

SOC. Yes; otherwise, my friend, they will find that things in motion are also things at rest, and it will be no more correct to say that all things are in motion than that all things are at rest.

THEO. What you say is very true.