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On The Heavens   

the manner of their motion and the kind of movement which is natural

to them. For if the various elements are constrained by one another to

move as they do, each must still have a natural movement which the

constrained contravenes, and the prime mover must cause motion not

by constraint but naturally. If there is no ultimate natural cause

of movement and each preceding term in the series is always moved by

constraint, we shall have an infinite process. The same difficulty

is involved even if it is supposed, as we read in the Timaeus, that

before the ordered world was made the elements moved without order.

Their movement must have been due either to constraint or to their

nature. And if their movement was natural, a moment's consideration

shows that there was already an ordered world. For the prime mover

must cause motion in virtue of its own natural movement, and the other

bodies, moving without constraint, as they came to rest in their

proper places, would fall into the order in which they now stand,

the heavy bodies moving towards the centre and the light bodies away

from it. But that is the order of their distribution in our world.

There is a further question, too, which might be asked. Is it possible

or impossible that bodies in unordered movement should combine in some

cases into combinations like those of which bodies of nature's

composing are composed, such, I mean, as bones and flesh? Yet this

is what Empedocles asserts to have occurred under Love. 'Many a head',

says he, 'came to birth without a neck.' The answer to the view that

there are infinite bodies moving in an infinite is that, if the

cause of movement is single, they must move with a single motion,

and therefore not without order; and if, on the other hand, the causes

are of infinite variety, their motions too must be infinitely

varied. For a finite number of causes would produce a kind of order,

since absence of order is not proved by diversity of direction in

motions: indeed, in the world we know, not all bodies, but only bodies

of the same kind, have a common goal of movement. Again, disorderly

movement means in reality unnatural movement, since the order proper

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