[
1074a]
[1]
there must be for
each of the other planets other spheres, one less in number than those
already mentioned, which counteract these and restore to the same
position the first sphere of the star which in each case is next in
order below.
1 In this way
only can the combination of forces produce the motion of the
planets.Therefore
since the forces by which the planets themselves are moved are 8 for
Jupiter and Saturn, and 25 for the others, and since of these the only
ones which do not need to be counteracted are those by which the
lowest planet
2
is moved, the counteracting spheres for the first two planets will be
6, and those of the remaining four will be 16; and the total number of
spheres, both those which move the planets and those which counteract
these, will be 55.If we
do not invest the moon and the sun with the additional motions which
we have mentioned,
3 there will be 47 (?)
4 spheres
in all.
This, then, may be taken to be
the number of the spheres; and thus it is reasonable to suppose that
there are as many immovable substances and principles,
5—the statement of logical necessity may
be left to more competent thinkers.
If there can be
no spatial motion which is not conducive to the motion of a
star,
[20]
and if moreover
every entity and every substance which is impassive and has in itself
attained to the highest good should be regarded as an end, then there
can be no other entity besides these,
6 and the number of the
substances must be as we have said. For if there are other substances,
they must move something, since they are the end of spatial
motion.But there
can be no other spatial motions besides those already mentioned. This
is a reasonable inference from a general consideration of spatial
motion. For if everything which moves exists for the sake of that
which is moved, and every motion for the sake of something which is
moved, no motion can exist for the sake of itself or of some other
motion, but all motions must exist for the sake of the
stars.For if we are
to suppose that one motion is for the sake of another, the latter too
must be for the sake of something else; and since the series cannot be
infinite, the end of every motion must be one of the divine bodies
which are moved through the heavens.
It
is evident that there is only one heaven.
7 For if there is to be a
plurality of heavens (as there is of men), the principle of each must
be one in kind but many in number.But all things which are many in number have
matter (for one and the same definition applies to many individuals,
e.g. that of "man"; but
Socrates is one
8), but the primary
essence has no matter, because it is complete reality. Therefore the
prime mover, which is immovable, is one both in formula and in number;
and therefore so also is that which is eternally and continuously in
motion. Therefore there is only one heaven.