[894a]
in everything to bring about generation? Obviously whenever a starting-principle receiving increase comes to the second change, and from this to the next, and on coming to the third admits of perception by percipients.1 Everything comes into being by this process of change and alteration; and a thing is really existent whenever it remains fixed, but when it changes into another constitution it is utterly destroyed.” Have we now, my friends, mentioned all the forms of motion, capable of numerical classification,2
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save only two?Clinias
What two?Athenian
Those, my good sir, for the sake of which, one may say, the whole of our present enquiry was undertaken.Clinias
Explain more clearly.Athenian
It was undertaken, was it not, for the sake of soul?Clinias
Certainly.Athenian
As one of the two let us count that motion which is always able to move other things, but unable to move itself; and that motion which always is able to move both itself and other things,—by way of combination and separation, of increase and decrease, of generation and corruption,—let us count as another separate unit
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in the total number of motions.Clinias
Be it so.Athenian
Thus we shall reckon as ninth on the list that motion which always moves another object and is moved by another; while that motion which moves both itself and another, and which is harmoniously adapted to all forms of action and passion, and is termed the real change and motion of all that really exists,—it, I presume, we shall call the tenth.
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Clinias
Most certainly.Athenian
Of our total of ten motions, which shall we most correctly adjudge to be the most powerful of all and excelling in effectiveness?Clinias
We are bound to affirm that the motion which is able to move itself excels infinitely, and that all the rest come after it.Athenian
Well said. Must we, then, alter one or two of the wrong statements we have now made?Clinias
Which do you mean?Athenian
Our statement about the tenth seems wrong.Clinias
How?Athenian
Logically it is first in point of origin and power; and the next one is second to it,
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although we absurdly called it ninth a moment ago.Clinias
What do you mean?Athenian
This: when we find one thing changing another, and this in turn another, and so on,—of these things shall we ever find one that is the prime cause of change? How will a thing that is moved by another ever be itself the first of the things that cause change? It is impossible. But when a thing that has moved itself changes another thing, and that other a third, and the motion thus spreads progressively through thousands upon thousands of things,
1 This account of the derivation of the sense-world from the “starting-principle” (ἀρχή) is obscure. It is generally interpreted as a “geometrical allegory,” the stages of development being from point to line, from line to surface, from surface to solid,—this last only being perceptible by the senses (cp. Aristot. Soul 404 b 18 ff.).
2 The 8 kinds of motion here indicated are—(1) circular motion round a fixed center; (2) locomotion (gliding or rolling); (3) combination; (4) separation; (5) increase; (6) decrease; (7) becoming; (8) perishing. The remaining two kinds (as described below) are—(9) other-affecting motion (or secondary causation); and (10) self-and-other-affecting motion (or primary causation).
Plato. Plato in Twelve Volumes, Vols. 10 & 11 translated by R.G. Bury. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1967 & 1968.
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