What then is movement? While belonging to a subject, it is something
by itself before belonging to a subject, as are quality, quantity,
and being. To begin with, nothing is predicated before it, and of
it, as a genus. Is change[417] anterior to movement? Here change is
identical with movement, or if change is to be considered a genus, it
will form a genus to be added to those already recognized. Besides, it
is evident that, on this hypothesis, movement will become a species,
and to it will be opposed, as another species, "generation," as,
for instance, "generation" is a change, but not a movement.[418]
Why then should generation not be a movement? Is it because what is
generated does not yet exist, and because movement could not exist in
non-being? Consequently, neither will generation be a change. Or is
this so because generation is an alteration and increase, and because
it presupposes that certain things are altered, and increase? To
speak thus is to busy ourselves with things that precede generation.
Generation presupposes production of some other form; for generation
does not consist in an alteration passively undergone, such as being
warmed, or being whitened; such effects could be produced before
realization of the generation. What then occurs in generation? There
is alteration. Generation consists in the production of an animal or
plant, in the reception of a form. Change is much more reasonably to
be considered a species, than movement; because the word change means
that one thing takes the place of another, while movement signifies
the actualization by which a being passes from what is proper to it,
to what is not, as in the translation from one place to another. If
that be not admitted (to define movement), it will at least have to be
acknowledged that the action of studying it, as that of playing the
lyre, and in general, all the movements that modify a habit, would
be subsumed within our definition. Alteration therefore could not be
anything else but a species of movement; since it is a movement which
produces passage from one state to another.[419]