The Complete Aristotle (eng.)

in the case of coming to be.
    Now the expression ‘not-being’ is used in several senses: and
there can be motion neither of that which ‘is not’ in respect of
the affirmation or negation of a predicate, nor of that which ‘is
not’ in the sense that it only potentially ‘is’, that is to say the
opposite of that which actually ‘is’ in an unqualified sense: for
although that which is ‘not-white’ or ‘not-good’ may nevertheless
he in motion accidentally (for example that which is ‘not-white’
might be a man), yet that which is without qualification
‘not-so-and-so’ cannot in any sense be in motion: therefore it is
impossible for that which is not to be in motion. This being so, it
follows that ‘becoming’ cannot be a motion: for it is that which
‘is not’ that ‘becomes’. For however true it may be that it
accidentally ‘becomes’, it is nevertheless correct to say that it
is that which ‘is not’ that in an unqualified sense ‘becomes’. And
similarly it is impossible for that which ‘is not’ to be at
rest.
    There are these difficulties, then, in the way of the assumption
that that which ‘is not’ can be in motion: and it may be further
objected that, whereas everything which is in motion is in space,
that which ‘is not’ is not in space: for then it would be
somewhere.
    So, too, ‘perishing’ is not a motion: for a motion has for its
contrary either another motion or rest, whereas ‘perishing’ is the
contrary of ‘becoming’.
    Since, then, every motion is a kind of change, and there are
only the three kinds of change mentioned above, and since of these
three those which take the form of ‘becoming’ and ‘perishing’, that
is to say those which imply a relation of contradiction, are not
motions: it necessarily follows that only change from subject to
subject is motion. And every such subject is either a contrary or
an intermediate (for a privation may be allowed to rank as a
contrary) and can be affirmatively expressed, as naked, toothless,
or black. If, then, the categories are severally distinguished as
Being, Quality, Place, Time, Relation, Quantity, and Activity or
Passivity, it necessarily follows that there are three kinds of
motion-qualitative, quantitative, and local.
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2
    In respect of Substance there is no motion, because Substance
has no contrary among things that are. Nor is there motion in
respect of Relation: for it may happen that when one correlative
changes, the other, although this does not itself change, is no
longer applicable, so that in these cases the motion is accidental.
Nor is there motion in respect of Agent and Patient-in fact there
can never be motion of mover and moved, because there cannot be
motion of motion or becoming of becoming or in general change of
change.
    For in the first place there are two senses in which motion of
motion is conceivable. (1) The motion of which there is motion
might be conceived as subject; e.g. a man is in motion because he
changes from fair to dark. Can it be that in this sense motion
grows hot or cold, or changes place, or increases or decreases?
Impossible: for change is not a subject. Or (2) can there be motion
of motion in the sense that some other subject changes from a
change to another mode of being, as e.g. a man changes from falling
ill to getting well? Even this is possible only in an accidental
sense. For, whatever the subject may be, movement is change from
one form to another. (And the same holds good of becoming and
perishing, except that in these processes we have a change to a
particular kind of opposite, while the other, motion, is a change
to a different kind.) So, if there is to be motion of motion, that
which is changing from health to sickness must simultaneously be
changing from this very change to another. It is clear, then, that
by the time that it has become sick, it must also have changed to
whatever may be the other change concerned (for that it should be
at rest, though logically possible, is excluded by the theory).
Moreover this other can never be any casual change, but must be a
change from something definite to some other definite thing. So in
this case it must be the opposite change, viz. convalescence. It is
only accidentally that there can be change of change, e.g. there is
a change from remembering to forgetting only because the subject of
this change changes at one time to knowledge, at another to
ignorance.
    In