XXIII. ELEMENTARY ATOMS.
AN elementary substance is an atom which, essentially composed of materia prima and substantial form, is simple, inasmuch as it does not result from a chemical combination of different substances. The word "atom" does not in itself indicate a smallest and indivisible substance, but a substance not constituted by aggregation of substances. This meaning is evidently right. An aggregate, though specifically one, cannot be called individually one, because it results from the union of many substances, whether their nature be the same, or not. By thus using the word "atom," we are in no danger of falling into what is called the atomic theory; for in that system, strictly speaking, the atoms are inert, of equal nature, essentially extended, only capable of moving and being moved, and quantitatively indivisible. But they are not so in the Physical system.
Applying then to elementary substances the known principles that we have pointed out, we must say that it is essentially composed of materia prima and substantial form. Being essentially extended, it must have the principle of extension; and the principle of extension is what we call materia prima. The substantial form is the principle of that virtue or activity which determines the specific nature of the substance, which principle cannot be essentially wanting in that elementary substance. Suppose, for instance, that oxygen, sulphur, hydrogen and carbon are, as we now believe them to be, elementary substances, specifically different. We learn their specific diversity from the divers and constant virtues, observable in their mutual operations, that chemistry shows plainly by facts within our reach: and we should look for them in vain elsewhere. Since therefore a specific activity is evident in these atoms, there must be a principle of that activity. But this is precisely what places them in different species, making the nature of hydrogen to be the nature of hydrogen, and not the nature of gold or of something else. There being then, in such atoms a principle of activity, we must admit a substantial form; that is, the said principle.
In discussing the principle of activity we have placed the elements in mutual relation: but that was for the purpose of making the argument more easily intelligible. If oxygen were the only thing in the corporeal world, it would have its materia prima and substantial form just as it has now when existing among other elementary substances; for with its extension it would have the principle of extension, and with its activity, (existing in potentia, at least,) it would have the principle of activity, i.e. the substantial form. We say in potentia, because, being inorganic, it could not operate on itself, so that if no other body of a different nature existed in the world, there would be no subject in which the potential activity could be brought into action.
The matter and form of the elements cannot be mingled in one principle. They are essentially two principles, really distinct. In this question we have to steer between two extremes, one of them sinning by excess, the other by defect. We should go into excess by imagining that materia prima is a substance constituted per se in its own being, and that every substantial form is a simple being, subsistent per se, and only operating on materia prima. Were it so, the form would not be substantial and informant, because it would not constitute the matter in substantial being. It would only be a forma assistens, not being by its own essence united to the matter, but only by the operation. In short, there the atom would have two complete substances in its own being, instead of being, as it is, one substance.
To consider the principles of extension and of activity as one being, in the absurd guise of a matter per se active or a force per se extended, would be sinning by defect.
Consequently we must affirm that in the elementary substances materia prima, though really distinct from the substantial form, is not separate from it. The true and philosophic meaning of these two expressions is well known. Two things are really separate when each has its complete being, and is the principle of its own operation. They are really distinct when each has a being per se incomplete, and each is not per se a principle of operation. Suppose, for instance, a waxen image of Caesar. The image is not separate from the wax, for the very wax is the image but distinct it is, because otherwise the wax could not be fashioned into any other image. But, between the pen that writes and the hand that holds it, there is something more than a real distinction; because the pen, though moved as an instrument by the hand, has a substantial and complete being, different from that of the hand. Here there is not a real distinction only. The pen is the separate instrument of the hand.
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