[
1066a]
[1]
For everything may sometimes be actual,
and sometimes not; e.g. the "buildable" qua
"buildable"; and the actualization of the "buildable" qua "buildable" is the act of
building.For the
actualization is either this—the act of
building—or a house. But when the house exists, it will no
longer be buildable; the buildable is that which is
being
built. Hence the actualization must be the act of building, and the
act of building is a kind of motion. The same argument applies to the
other kinds of motion.
That this account is correct
is clear from what the other authorities say about motion, and from
the fact that it is not easy to define it otherwise. For one thing, it
could not be placed in any other class; this is clear from the fact
that some people
1 identify it
with otherness and inequality and not-being, none of which is
necessarily moved;moreover
change is no more into these or out of them than into or out of their
opposites.
2 The reason for placing motion in this class
is that it is considered to be indeterminate, and the principles in
one of the columns of contraries are indeterminate, being privative;
for none of them is a determinate thing or quality or any of the other
categories.The
reason for considering motion to be indeterminate is that it cannot be
associated either with the potentiality or with the actuality of
things; for neither that which is potentially
[20]
nor that which is actually of a certain
size is necessarily moved.And motion is considered to be a kind of actualization, but
incomplete
3; the reason of this is that the
potential, of which it is the actualization, is incomplete.
Thus it is difficult to comprehend what
motion is; for we must associate it either with privation or with
potentiality or with absolute actuality; and apparently none of these
is possible.There
remains, then, the account which we have given; that it is an
actuality, and an actuality of the kind which we have described, which
is hard to visualize but capable of existing.
That motion is in the movable is evident; for it is
the complete realization of the movable by that which is capable of
causing motion, and the actualization of that which is capable of
causing motion is identical with that of the movable.For it must be a complete
realization of them both; since a thing is capable of moving because
it has the potentiality, but it moves only when it is active; but it
is upon the movable that it is capable of acting. Thus the actuality
of both alike is one; just as there is the same interval from one to
two as from two to one, and the hill up and the hill down are one,
although their
being is not one; the case of the mover
and the thing moved is similar.
4The infinite is either (a) that which
cannot be traversed because it is not its nature to be traversed (just
as sound is by nature invisible); or (b) that which admits of an
endless traverse; or (c) scarcely admits of traverse; or (d) which,
though it would naturally admit of traverse or limit, does not do so.