That a quantity really distinct from a substance may not be a subject of qualities could be confirmed not only by the testimony of the Holy Fathers but also of the philosophers. Therefore, let it suffice to adduce Aristotle, the Prince of philosophers. However, he says in the Categories that substance alone is susceptive of contraries through a change of itself; and he says that this is properly characteristic of substance. But if there could be between substance and qualities one intermediate quantity differing and sustaining sensual and corporeal qualities, it is manifest that that quantity would be susceptive of contraries through a proper change of itself. For that would at one time be sweet, at another time would be bitter, when it would support whiteness, when it would support blackness, when it would be warm, and when it would be cold; and so a thing other than a substance would be susceptive of contraries through a change of itself.
Again, according to the same philosopher alteration as regards a sensible quality is distinguished from condensation and rarefaction to such a degree that, when any body is rarified or condensed, it is not necessary that it lose all its qualities. Therefore, a white body may become rarified; and, when this has been done, it can not be granted that it may lose the prior whiteness and may have a new whiteness; for there is here nothing efficient enough that would be able to induce whiteness into this body. But this can not obtain if quantity be a thing intermediate between substance and qualities; for, if it be an intermediate thing, it is necessary that a rarefied substance have a new quantity, as will be said and shown later. But since the newness of its accident may follow in consequence of the newness of the subject, it is necessary that whiteness should be new and for the same reason each quality existing subjectively in that quantity would be new.
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