10. If matter could be affected, it would have to preserve some of
the affection, retaining either the affection itself, or remain in a
state different from the one in which it was before it was affected.
But when one quality appears after another quality, it is no longer
matter that receives it, but matter as determined by a quality. If even
this quality should evanesce, though leaving some trace of itself by
the action it has exercised, the substrate will still more be altered;
proceeding thus it will come to be something entirely different from
pure matter, it will be something multiple by its forms and by its
manners of existence. It will no longer be the common receptacle of all
things, since it will contain an obstacle to many things that could
happen to it; matter would no longer subsist within it, and would no
longer be incorruptible. Now if, by definition, matter always remains
what it was since its origin, namely "matter," then, if we insist
that it be altered, it is evident that matter no longer remains such.
Moreover, if everything that is altered must remain unchanged in kind,
so as not to be changed in itself, though changed in accidents; in one
word, if that which is changed must be permanent, and if that which is
permanent be not that which is affected, we come to a dilemma; either
matter is altered, and abandons its nature; or it does not abandon its
nature, and is not changed. If we say that matter is changed, but not
in so far as it is matter, it will, to begin with, be impossible to
state in what it is changed; and further, we would thereby be forced
to insist it was not changed. Indeed, just as other things, which are
forms, cannot be changed in their "being" (or, nature), because it is
this very unalterability which constitutes their "being" (or, nature),
likewise, as the "being" (or, nature) of matter is to exist in so far
as it is matter, it cannot be altered in so far as it is matter, and
it must necessarily be permanent in this respect. Therefore if form be
unalterable, matter must be equally unalterable.