JMC : The Physical System of St. Thomas / by G.M. Cornoldi, S.J.


THERE is not much difficulty in proving that between the materia prima and the substantial form of an atom there truly is a real distinction. Matter is in its essence passive; while the principle of activity, which the form is, is active. But the relation of the active to the passive is contradictory. Therefore they cannot meet in one being by virtue of one same principle. Hence an atom, being constituted of matter and form, has two principles really distinct from each other.

Secondly, all existing bodies must have density and a determinate figure. The theory of crystallization is founded on that. Now what is the intrinsic cause by which a body, and likewise an atom, has this or that density instead of another? Matter is not the cause of it, being of itself undetermined. Therefore the form is the cause of it. Hence the form is the determining principle, and the matter is the determined principle. This necessarily implies a real distinction. St. Thomas remarks that matter without a form could not be constituted into an atom, i.e. into an indivisible substance, in which the parts, though not divided, are really distinct. Omne corpus divisibile est, he says. Omne autem divisibile indiget aliquo continente et uniente partes ejus. To make this clear, we have only to observe what takes place in plants, in brutes and in man. Whence does their structure, order, and density proceed? Not from matter; for without the vital principle by which it is informed, and from which it is really distinct, materia prima is indifferent to every structure, order and density, and when deprived of the vital principle, loses the density, order and figure that it had. Therefore all this proceeds from the same principle that informs the body of the living being. The same reasoning holds good about the forms of the elements in relation to the matter which they inform, viz., that the form and the matter of each element are really distinct.

Thirdly, extension and quantity, like activity and force, are a mode of the elementary atom's being. Now the mode must be in proportion to the modified principle; and therefore the principle of extension is extended, the principle of activity active.

But there is a real distinction between extension and force. Therefore there is a real distinction between the principle of extension, which is matter, and the principle of force, which is form. This is always the way of arguing in philosophy, when treating of acts and of the principles from which they are derived: for, whenever we perceive diversity of acts, we infer diversity of the immediate potentiae, which are their proximate principles.

Here again a comparison will be useful. Suppose that you are pushing some sort of body with your whole hand. In doing so you feel a force that presses and operates on an extended thing, because that which pushes is not a mathematical point, but the whole hand: and hence we deduce with certainty that in the hand there must be, besides the extended matter, a principle of force by which the matter presses that body. Again, when we feel heat, our sensation is evidently a mode of two principles really distinct, from one of which, i.e. the matter, we have extended being, and from the other, i.e. the anima, we have the vital affection. In like manner the force manifested by an elementary atom is not in a mathematical point, but in an extended thing: and therefore if the force demonstrates to you a principle of activity, its being in an extended thing shows you the principle of extension really distinct from the principle of activity.

Fourthly, we can find in the natural disposition of simple bodies a proof not without its value. In fact a substance that in its completed essence is simple will certainly not have parts outside of parts. Wherever it is, the whole of it will be; or to use a well-known adage, the whole will be in the whole and in each part. Now this simple substance is per se subsistent and therefore per se not divisible: but that which is per se not divisible cannot be per se extended. Therefore a substance that is per se simple and subsistent cannot be per se extended. So that, unless we deny the real extension of corporeal substances, we must admit that the principles of activity, which the forms are -- or as some people call them, forces -- receive their being, as extended and divisible things, from another and a different principle, which, being the principle of extension, is matter precisely.

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