The Complete Aristotle (eng.)

and this is altered by sensible objects: for all moral
excellence is concerned with bodily pleasures and pains, which
again depend either upon acting or upon remembering or upon
anticipating. Now those that depend upon action are determined by
sense-perception, i.e. they are stimulated by something sensible:
and those that depend upon memory or anticipation are likewise to
be traced to sense-perception, for in these cases pleasure is felt
either in remembering what one has experienced or in anticipating
what one is going to experience. Thus all pleasure of this kind
must be produced by sensible things: and since the presence in any
one of moral defect or excellence involves the presence in him of
pleasure or pain (with which moral excellence and defect are always
concerned), and these pleasures and pains are alterations of the
sensitive part, it is evident that the loss and acquisition of
these states no less than the loss and acquisition of the states of
the body must be the result of the alteration of something else.
Consequently, though their becoming is accompanied by an
alteration, they are not themselves alterations.
    Again, the states of the intellectual part of the soul are not
alterations, nor is there any becoming of them. In the first place
it is much more true of the possession of knowledge that it depends
upon a particular relation. And further, it is evident that there
is no becoming of these states. For that which is potentially
possessed of knowledge becomes actually possessed of it not by
being set in motion at all itself but by reason of the presence of
something else: i.e. it is when it meets with the particular object
that it knows in a manner the particular through its knowledge of
the universal. (Again, there is no becoming of the actual use and
activity of these states, unless it is thought that there is a
becoming of vision and touching and that the activity in question
is similar to these.) And the original acquisition of knowledge is
not a becoming or an alteration: for the terms ‘knowing’ and
‘understanding’ imply that the intellect has reached a state of
rest and come to a standstill, and there is no becoming that leads
to a state of rest, since, as we have said above, change at all can
have a becoming. Moreover, just as to say, when any one has passed
from a state of intoxication or sleep or disease to the contrary
state, that he has become possessed of knowledge again is incorrect
in spite of the fact that he was previously incapable of using his
knowledge, so, too, when any one originally acquires the state, it
is incorrect to say that he becomes possessed of knowledge: for the
possession of understanding and knowledge is produced by the soul’s
settling down out of the restlessness natural to it. Hence, too, in
learning and in forming judgements on matters relating to their
sense-perceptions children are inferior to adults owing to the
great amount of restlessness and motion in their souls. Nature
itself causes the soul to settle down and come to a state of rest
for the performance of some of its functions, while for the
performance of others other things do so: but in either case the
result is brought about through the alteration of something in the
body, as we see in the case of the use and activity of the
intellect arising from a man’s becoming sober or being awakened. It
is evident, then, from the preceding argument that alteration and
being altered occur in sensible things and in the sensitive part of
the soul, and, except accidentally, in nothing else.
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4
    A difficulty may be raised as to whether every motion is
commensurable with every other or not. Now if they are all
commensurable and if two things to have the same velocity must
accomplish an equal motion in an equal time, then we may have a
circumference equal to a straight line, or, of course, the one may
be greater or less than the other. Further, if one thing alters and
another accomplishes a locomotion in an equal time, we may have an
alteration and a locomotion equal to one another: thus an affection
will be equal to a length, which is impossible. But is it not only
when an equal motion is accomplished by two things in an equal time
that the velocities of the two are equal? Now an affection cannot
be equal to a length. Therefore there cannot be an alteration equal
to or less than a locomotion: and consequently it is not the case
that every motion is commensurable