On The Heavens   

of our inquiry. (a) In one sense, then, we call 'heaven' the substance

of the extreme circumference of the whole, or that natural body

whose place is at the extreme circumference. We recognize habitually a

special right to the name 'heaven' in the extremity or upper region,

which we take to be the seat of all that is divine. (b) In another

sense, we use this name for the body continuous with the extreme

circumference which contains the moon, the sun, and some of the stars;

these we say are 'in the heaven'. (c) In yet another sense we give the

name to all body included within extreme circumference, since we

habitually call the whole or totality 'the heaven'. The word, then, is

used in three senses.

Now the whole included within the extreme circumference must be

composed of all physical and sensible body, because there neither

is, nor can come into being, any body outside the heaven. For if there

is a natural body outside the extreme circumference it must be

either a simple or a composite body, and its position must be either

natural or unnatural. But it cannot be any of the simple bodies.

For, first, it has been shown that that which moves in a circle cannot

change its place. And, secondly, it cannot be that which moves from

the centre or that which lies lowest. Naturally they could not be

there, since their proper places are elsewhere; and if these are there

unnaturally, the exterior place will be natural to some other body,

since a place which is unnatural to one body must be natural to

another: but we saw that there is no other body besides these. Then it

is not possible that any simple body should be outside the heaven.

But, if no simple body, neither can any mixed body be there: for the

presence of the simple body is involved in the presence of the

mixture. Further neither can any body come into that place: for it

will do so either naturally or unnaturally, and will be either

simple or composite; so that the same argument will apply, since it

makes no difference whether the question is 'does A exist?' or

'could A come to exist?' From our arguments then it is evident not