HKB
resist the action of natural heat, and prevent the consumption of the "radical humor"; just as lead or tin is mixed with silver to prevent its being consumed by fire.
But this is unreasonable in many ways. Firstly, because it comes to the same that a form can be produced in another matter, or that it can cease to be in its proper matter; wherefore all things that can be generated are corruptible, and conversely. Now it is manifest that the human form can cease to exist in this (particular) matter which is its subject: else the human body would not be corruptible. Consequently it can begin to exist in another matter, so that something else be changed into true human nature. Secondly, because in all beings whose entire matter is contained in one individual there is only one individual in the species: as is clearly the case with the sun, moon and such like. Thus there would only be one individual of the human species. Thirdly, because multiplication of matter cannot be understood otherwise than either in respect of quantity only, as in things which are rarefied, so that their matter increases in dimensions; or in respect of the substance itself of the matter. But as long as the substance alone of matter remains, it cannot be said to be multiplied; for multitude cannot consist in the addition of a thing to itself, since of necessity it can only result from division. Therefore some other substance must be added to matter, either by creation, or by something else being changed into it. Consequently no matter can be multiplied save either by rarefaction as when air is made from water; or by the change of some other things, as fire is multiplied by the addition of wood; or lastly by creation. Now it is manifest that the multiplication of matter in the human body does not occur by rarefaction: for thus the body of a man of perfect age would be more imperfect than the body of a child. Nor does it occur by creation of fresh matter: for, according to Gregory (Moral. xxxii): "All things were created together as to the substance of matter, but not as to the specific form." Consequently the multiplication of the human body can only be the result of the food being changed into the true human nature. Fourthly, because, since man does not differ from animals and plants in regard to the vegetative soul, it would follow that the bodies of animals and plants do not increase through a change of nourishment into the body so nourished, but through some kind of multiplication. Which multiplication cannot be natural: since the matter cannot naturally extend beyond a certain fixed quantity; nor again does anything increase naturally, save either by rarefaction or the change of something else into it. Consequently the whole process of generation and nourishment, which are called "natural forces," would be miraculous. Which is altogether inadmissible.