The second is that a molecule is one owing to the oneness of the common tie between its constituent elements, and to their common and stable dependence on one mechanical law. Hence a molecule is not one substance, but one compound nature involving a number of substances conspiring to form a permanent principle of actions and passions of a certain kind. In other terms, a molecule is not unum substantiale, but unum essentiale or unum naturale.
The third is that the specific form of a molecule admits of different degrees within the limits of its species. This conclusion was quite unknown to the followers of Aristotle; and S. Thomas reprehends Averroës for having said that the forms of the elements (fire, water, air, and earth) could pass through different degrees of perfection, whilst Aristotle teaches that they are in indivisibili, and that every change in the form changes the specific essence.[64] Yet it is evident that as there can be circles, ellipses, and other curves having a different degree of curvature, while preserving the same specific form, so also can molecules admit of a different degree of closeness in their constitution without trespassing on the limits of their species. So long as the changes made in a molecule do not interfere with the conditions on which the form of its equations depends, so long the specific constitution of the molecule remains unimpaired. Mathematical formulas are only artificial abridgments of metaphysical expressions; and their accidental changes express but the accidental changes of the thing which they represent. On the other hand, it is well known that the equations by which the specific constitution of a compound system is determined can preserve the same form, while some of the quantities they contain receive an increase or a decrease connected with a change of merely accidental conditions.
The fourth conclusion is that a number of primitive molecules of different kinds may combine together in such a manner as to impair more or less their own individuality by fixing themselves in a new molecular system of greater complexity. Likewise, a molecular system of greater complexity is susceptible of resolution into less complex systems. These combinations and resolutions are the proper object of chemistry, which is the science of the laws, principles, and conditions of the specific changes of natural substances, and to which metaphysicians must humbly refer when treating of substantial generation, if they wish to reason on the solid ground of facts.
We have thus briefly stated what we hold to be the true scientific and philosophic view of the constitution of natural substances; and as we have carefully avoided all gratuitous assumptions, we feel confident that our readers need no further arguments to be convinced of its value as compared with the hypothetical views of the old physicists. As, however, the conclusions of the peripatetic school concerning the constitution and generation of natural substances have still some ardent supporters, who think that the strictly substantial generations and corruptions are demonstrated by unanswerable arguments, we have yet to show that such pretended arguments consist of mere assumption and equivocation.
The first argument in favor of the old theory may be presented under the following form: “Every natural substance is unum per se—that is, substantially one. Therefore no natural substance implies more than one substantial form.” The antecedent is assumed as evident, and the consequent is proved by the principle that “from two beings in act it is impossible to obtain a being substantially one.” Hence it is concluded that all natural substances, as water, flesh, iron, etc., have a substantial form which gives to the first matter the being of water, of flesh, of iron, etc.
This argument, instead of proving the truth of the theory, proves its weakness; for it consists of a petitio principii. What right has the peripatetic school to assume that every natural substance is unum per se substantially? A substance physically simple is, of course, unum per se substantially; but water, flesh, iron, and the other natural substances are not physically simple, since they imply quantity of mass and quantity of volume, which presuppose a number of material terms actually distinct, and therefore possessing their distinct substantial forms. No compound substance can be unum per se as a substance; it can be unum per se only as a compound essence; and for this reason every natural substance contains as many substantial forms as it contains primitive elements, whereas it has only one essential form, which gives the first being to its compound nature. This one essential form is, as we have explained, the specific composition of its constituent elements.
The principle “From two beings in act it is impossible to obtain a being substantially one” is perfectly true; but it will be false if, instead of “substantially,” we put “essentially”; for all essences physically compounded result from the union of a certain number of actual beings, and yet every compound essence is unum per se essentially, though not substantially. For, as unum per accidens is that which has something superadded to its essential principles, so unum per se is that which includes nothing in itself but its essential principles; and consequently every essence, as such, is unum per se, whether it be physically simple or not—that is, whether it be one substance or a number of substances conspiring into a specific compound. Hence flesh, water, iron, and every other natural substance may be, and are, unum per se, notwithstanding the fact that they consist of a number of primitive elements and contain as many substantial forms as components.
It is therefore manifest that this first argument has no strength. No ancient or modern philosopher has ever proved that any natural substance is substantially one. To prove such an assertion it would be necessary to show that the physical compound is physically simple; which, we trust, no one will attempt to show. Even Liberatore, whose efforts to revive among us the peripatetic theory have been so remarkable, seems to have felt the utter impossibility of substantiating such an arbitrary supposition by anything like a proof, as he lays it down without even pretending to investigate its value. “True bodies,” says he—“that is, bodies which are substances, and not mere aggregates of substances—are essentially constituted of matter and substantial form.”[65] Indeed, if a body is not an aggregate of substances, it must be evident to every one that the essence of that body is exclusively constituted of matter and substantial form. But where is a body to be found which is not an aggregate of substances—that is, of primitive elements? The learned author omits to examine this essential point, clearly because there are neither facts in science nor arguments in philosophy by which it can be settled favorably to the peripatetic view. Thus the whole theory of substantial generations, understood in the peripatetic sense, rests on a mere assumption contradicted, as we know, by natural science no less than by metaphysical reasoning.
The second argument of the peripatetic school is as follows: When the matter has its first being, all form supervening to it is accidental; for the matter which has its first being cannot receive but a being secundum quid—that is, a mode of being which is an accident. But the natural substance cannot be constituted by an accidental form. Therefore the form of the natural substance does not supervene to any matter having its first being, but itself gives the first being to its matter, and therefore is a strictly substantial form.
Our answer is very plain. We admit that, when the matter has its first being, all supervening form is accidental to it; and we admit, also, that the composition of matter with matter is an accidental entity, and gives to the matter an accidental mode of being. This, however, does not mean that the specific composition is an accidental form of the compound nature. Composition, as compared with substance, is an accident; but, as compared with the essence of the compound, is an essential constituent, as we have already remarked; for it is of the essence of all physical compounds to have a number of substances as their matter, and a specific composition as their form. In other terms, the essence of a physical compound involves substance and accident alike; but what is an accident of the component substances is not an accident of the compound essence. Hence the proposition, “The natural substance cannot be constituted by an accidental form,” must be distinguished. If “natural substance” stands for the primitive substances that constitute the matter of the compound nature, the proposition is true; for all such substances have their strictly substantial forms, as is obvious. If “natural substance” stands for the compound nature itself, inasmuch as it is a compound of a certain species, then the proposition must be subdistinguished. For, if by “accidental form” we understand an accident of the component substances, the proposition will be false; for, evidently, the compound nature is constituted by composition, and composition is an accident of the components. Whilst, if the words “accidental form” are meant to express an accident of the compound nature, then the proposition is true again; for the composition is not an accidental, but an essential, constituent of the compound, as every one must concede. Yet “essential” is not to be confounded with “substantial”; and therefore, though all natural substances must have their essential form, it does not follow that such a form gives the first being to the matter, but only that it gives the first being to the specific compound inasmuch as it is such a compound. Had the peripatetics kept in view, when treating of natural substances, the necessary distinction between the essential and the strictly substantial forms, they would possibly have concluded, with the learned Card. Tolomei, that their theory was “a groundless assumption,” and their arguments a “begging the question.” But, unfortunately, Aristotle’s authority, before the discoveries of modern science, had such a weight with our forefathers that they scarcely dared to question what they believed to be the cardinal point of his philosophy. But let us go on.