in due proportion to larger and lesser circles.  ‘Very true.’  And when you speak of bodies moving in many places, you seem to me to mean those which move from one place to another, and sometimes have one centre of motion and sometimes more than one because they turn upon their axis; and whenever they meet anything, if it be stationary, they are divided by it; but if they get in the midst between bodies which are approaching and moving towards the same spot from opposite directions, they unite with them.  ‘I admit the truth of what you are saying.’  Also when they unite they grow, and when they are divided they waste away—­that is, supposing the constitution of each to remain, or if that fails, then there is a second reason of their dissolution.  ’And when are all things created and how?’ Clearly, they are created when the first principle receives increase and attains to the second dimension, and from this arrives at the one which is neighbour to this, and after reaching the third becomes perceptible to sense.  Everything which is thus changing and moving is in process of generation; only when at rest has it real existence, but when passing into another state it is destroyed utterly.  Have we not mentioned all motions that there are, and comprehended them under their kinds and numbered them with the exception, my friends, of two?

Cleinias:  Which are they?

Athenian:  Just the two, with which our present enquiry is concerned.

Cleinias:  Speak plainer.

Athenian:  I suppose that our enquiry has reference to the soul?

Cleinias:  Very true.

Athenian:  Let us assume that there is a motion able to move other things, but not to move itself; that is one kind; and there is another kind which can move itself as well as other things, working in composition and decomposition, by increase and diminution and generation and destruction—­ that is also one of the many kinds of motion.

Cleinias:  Granted.

Athenian:  And we will assume that which moves other, and is changed by other, to be the ninth, and that which changes itself and others, and is coincident with every action and every passion, and is the true principle of change and motion in all that is—­that we shall be inclined to call the tenth.

Cleinias:  Certainly.

Athenian:  And which of these ten motions ought we to prefer as being the mightiest and most efficient?

Cleinias:  I must say that the motion which is able to move itself is ten thousand times superior to all the others.

Athenian:  Very good; but may I make one or two corrections in what I have been saying?

Cleinias:  What are they?

Athenian:  When I spoke of the tenth sort of motion, that was not quite correct.

Cleinias:  What was the error?

Athenian:  According to the true order, the tenth was really the first in generation and power; then follows the second, which was strangely enough termed the ninth by us.