continue to be in motion when their movent is no longer in contact
with them? If we say that the movent in such cases moves something
else at the same time, that the thrower e.g. also moves the air, and
that this in being moved is also a movent, then it would be no more
possible for this second thing than for the original thing to be in
motion when the original movent is not in contact with it or moving
it: all the things moved would have to be in motion simultaneously and
also to have ceased simultaneously to be in motion when the original
movent ceases to move them, even if, like the magnet, it makes that
which it has moved capable of being a movent. Therefore, while we must
accept this explanation to the extent of saying that the original
movent gives the power of being a movent either to air or to water
or to something else of the kind, naturally adapted for imparting
and undergoing motion, we must say further that this thing does not
cease simultaneously to impart motion and to undergo motion: it ceases
to be in motion at the moment when its movent ceases to move it, but
it still remains a movent, and so it causes something else consecutive
with it to be in motion, and of this again the same may be said. The
motion begins to cease when the motive force produced in one member of
the consecutive series is at each stage less than that possessed by
the preceding member, and it finally ceases when one member no
longer causes the next member to be a movent but only causes it to
be in motion. The motion of these last two-of the one as movent and of
the other as moved-must cease simultaneously, and with this the
whole motion ceases. Now the things in which this motion is produced
are things that admit of being sometimes in motion and sometimes at
rest, and the motion is not continuous but only appears so: for it
is motion of things that are either successive or in contact, there
being not one movent but a number of movents consecutive with one
another: and so motion of this kind takes place in air and water. Some
say that it is 'mutual replacement': but we must recognize that the
difficulty raised cannot be solved otherwise than in the way we have
described. So far as they are affected by 'mutual replacement', all
the members of the series are moved and impart motion
simultaneously, so that their motions also cease simultaneously: but
our present problem concerns the appearance of continuous motion in
a single thing, and therefore, since it cannot be moved throughout its
motion by the same movent, the question is, what moves it?

  Resuming our main argument, we proceed from the positions that there
must be continuous motion in the world of things, that this is a
single motion, that a single motion must be a motion of a magnitude
(for that which is without magnitude cannot be in motion), and that
the magnitude must be a single magnitude moved by a single movent (for
otherwise there will not be continuous motion but a consecutive series
of separate motions), and that if the movement is a single thing, it
is either itself in motion or itself unmoved: if, then, it is in
motion, it will have to be subject to the same conditions as that
which it moves, that is to say it will itself be in process of
change and in being so will also have to be moved by something: so
we have a series that must come to an end, and a point will be reached
at which motion is imparted by something that is unmoved. Thus we have
a movent that has no need to change along with that which it moves but
will be able to cause motion always (for the causing of motion under
these conditions involves no effort): and this motion alone is
regular, or at least it is so in a higher degree than any other, since
the movent is never subject to any change. So, too, in order that
the motion may continue to be of the same character, the moved must
not be subject to change in respect of its relation to the movent.
Moreover the movent must occupy either the centre or the
circumference, since these are the first principles from which a
sphere is derived. But the things nearest the movent are those whose
motion is quickest, and in this case it is the motion of the
circumference that is the quickest: therefore the movent occupies
the circumference.

  There is a further difficulty in supposing it to be possible for
anything that is in motion to cause motion continuously and not merely
in the way in which it is caused by something repeatedly pushing (in
which case the continuity amounts to no more than successiveness).
Such a movent must either itself continue to push or pull or perform
both these actions, or else the action must be taken up by something
else and be passed on from one movent to another (the process that
we described before as occurring in the case of things thrown, since
the air or the water, being divisible, is a movent only in virtue of
the fact that different parts of the air are moved one after another):
and in either case the motion cannot be a single motion, but only a
consecutive series of motions. The only continuous motion, then, is
that which is caused by the unmoved movent: and this motion is
continuous because the movent remains always invariable, so that its
relation to that which it moves remains also invariable and
continuous.

  Now that these points are settled, it is clear that the first
unmoved movent cannot have any magnitude. For if it has magnitude,
this must be either a finite or an infinite magnitude. Now we have
already'proved in our course on Physics that there cannot be an
infinite magnitude: and we have now proved that it is impossible for a
finite magnitude to have an infinite force, and also that it is
impossible for a thing to be moved by a finite magnitude during an
infinite time. But the first movent causes a motion that is eternal
and does cause it during an infinite time. It is clear, therefore,
that the first movent is indivisible and is without parts and
without magnitude.

                                   -THE END-
.