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Works by Aristotle
Pages of Metaphysics

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has been shown also that this substance cannot have any magnitude, but
is without parts and indivisible (for it produces movement through
infinite time, but nothing finite has infinite power; and, while every
magnitude is either infinite or finite, it cannot, for the above
reason, have finite magnitude, and it cannot have infinite magnitude
because there is no infinite magnitude at all). But it has also been
shown that it is impassive and unalterable; for all the other
changes are posterior to change of place.

It is clear, then, why these things are as they are. But we must
not ignore the question whether we have to suppose one such
substance or more than one, and if the latter, how many; we must
also mention, regarding the opinions expressed by others, that they
have said nothing about the number of the substances that can even
be clearly stated. For the theory of Ideas has no special discussion
of the subject; for those who speak of Ideas say the Ideas are
numbers, and they speak of numbers now as unlimited, now as limited by
the number 10; but as for the reason why there should be just so
many numbers, nothing is said with any demonstrative exactness. We
however must discuss the subject, starting from the presuppositions
and distinctions we have mentioned. The first principle or primary
being is not movable either in itself or accidentally, but produces
the primary eternal and single movement. But since that which is moved
must be moved by something, and the first mover must be in itself
unmovable, and eternal movement must be produced by something
eternal and a single movement by a single thing, and since we see that
besides the simple spatial movement of the universe, which we say
the first and unmovable substance produces, there are other spatial
movements-those of the planets-which are eternal (for a body which
moves in a circle is eternal and unresting; we have proved these
points in the physical treatises), each of these movements also must
be caused by a substance both unmovable in itself and eternal. For the
nature of the stars is eternal just because it is a certain kind of
substance, and the mover is eternal and prior to the moved, and that
which is prior to a substance must be a substance. Evidently, then,
there must be substances which are of the same number as the movements
of the stars, and in their nature eternal, and in themselves
unmovable, and without magnitude, for the reason before mentioned.
That the movers are substances, then, and that one of these is first
and another second according to the same order as the movements of the
stars, is evident. But in the number of the movements we reach a
problem which must be treated from the standpoint of that one of the
mathematical sciences which is most akin to philosophy-viz. of
astronomy; for this science speculates about substance which is
perceptible but eternal, but the other mathematical sciences, i.e.
arithmetic and geometry, treat of no substance. That the movements are
more numerous than the bodies that are moved is evident to those who
have given even moderate attention to the matter; for each of the
planets has more than one movement. But as to the actual number of
these movements, we now-to give some notion of the subject-quote
what some of the mathematicians say, that our thought may have some
definite number to grasp; but, for the rest, we must partly
investigate for ourselves, Partly learn from other investigators,
and if those who study this subject form an opinion contrary to what
we have now stated, we must esteem both parties indeed, but follow the
more accurate.
Eudoxus supposed that the motion of the sun or of the moon
involves, in either case, three spheres, of which the first is the
sphere of the fixed stars, and the second moves in the circle which
runs along the middle of the zodiac, and the third in the circle which
is inclined across the breadth of the zodiac; but the circle in
which the moon moves is inclined at a greater angle than that in which
the sun moves. And the motion of the planets involves, in each case,

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