IF FORM BE UNCHANGEABLE, SO IS MATTER.
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.