The Complete Aristotle (eng.)

proceed simultaneously
(for the movent is causing motion and the moved is being moved
simultaneously) it is evident that the respective motions of A, B,
G, and each of the other moved movents are simultaneous. Let us
take the motion of each separately and let E be the motion of A, Z
of B, and H and O respectively the motions of G and D: for though
they are all moved severally one by another, yet we may still take
the motion of each as numerically one, since every motion is from
something to something and is not infinite in respect of its
extreme points. By a motion that is numerically one I mean a motion
that proceeds from something numerically one and the same to
something numerically one and the same in a period of time
numerically one and the same: for a motion may be the same
generically, specifically, or numerically: it is generically the
same if it belongs to the same category, e.g. substance or quality:
it is specifically the same if it proceeds from something
specifically the same to something specifically the same, e.g. from
white to black or from good to bad, which is not of a kind
specifically distinct: it is numerically the same if it proceeds
from something numerically one to something numerically one in the
same period of time, e.g. from a particular white to a particular
black, or from a particular place to a particular place, in a
particular period of time: for if the period of time were not one
and the same, the motion would no longer be numerically one though
it would still be specifically one.
    We have dealt with this question above. Now let us further take
the time in which A has completed its motion, and let it be
represented by K. Then since the motion of A is finite the time
will also be finite. But since the movents and the things moved are
infinite, the motion EZHO, i.e. the motion that is composed of all
the individual motions, must be infinite. For the motions of A, B,
and the others may be equal, or the motions of the others may be
greater: but assuming what is conceivable, we find that whether
they are equal or some are greater, in both cases the whole motion
is infinite. And since the motion of A and that of each of the
others are simultaneous, the whole motion must occupy the same time
as the motion of A: but the time occupied by the motion of A is
finite: consequently the motion will be infinite in a finite time,
which is impossible.
    It might be thought that what we set out to prove has thus been
shown, but our argument so far does not prove it, because it does
not yet prove that anything impossible results from the contrary
supposition: for in a finite time there may be an infinite motion,
though not of one thing, but of many: and in the case that we are
considering this is so: for each thing accomplishes its own motion,
and there is no impossibility in many things being in motion
simultaneously. But if (as we see to be universally the case) that
which primarily is moved locally and corporeally must be either in
contact with or continuous with that which moves it, the things
moved and the movents must be continuous or in contact with one
another, so that together they all form a single unity: whether
this unity is finite or infinite makes no difference to our present
argument; for in any case since the things in motion are infinite
in number the whole motion will be infinite, if, as is
theoretically possible, each motion is either equal to or greater
than that which follows it in the series: for we shall take as
actual that which is theoretically possible. If, then, A, B, G, D
form an infinite magnitude that passes through the motion EZHO in
the finite time K, this involves the conclusion that an infinite
motion is passed through in a finite time: and whether the
magnitude in question is finite or infinite this is in either case
impossible. Therefore the series must come to an end, and there
must be a first movent and a first moved: for the fact that this
impossibility results only from the assumption of a particular case
is immaterial, since the case assumed is theoretically possible,
and the assumption of a theoretically possible case ought not to
give rise to any impossible result.
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2
    That which is the first movement of a thing-in the sense that it
supplies not ‘that for the sake of which’ but the source of the
motion-is always together with that which is moved by it by
‘together’ I mean that there is nothing intermediate