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


OF these very little is said in modern schools of physics or of philosophy; and yet the doctrine about it is so important, that without it the physical system would be untenable, and all nature would appear to the mind to be full, not only of inexplicable puzzles, but also of evident contradictions. Let us begin by asking this question: Suppose that we acknowledge the complete and highest Being of God, yet deny His operation. What could we then say about His knowing, loving, creating? What sort of conception could we form of that most perfect Nature? Either none at all, or the conception of an absurdity.

As God is the complete and most perfect Being (esse), so in Him there is not any real difference between being and the power to do and the action itself. He is the One most pure, most simple, most complete, most perfect ACT. But it is not so with created substances, especially corporeal ones, with which we are now more particularly concerned. They have indeed a likeness to God, inasmuch as they have being, and have power to act, and do act; but, by reason of their imperfection, there necessarily is a real distinction between their being, their power to act and their action. Moreover, since God is most perfect and the source of all being, He never can receive from His creatures anything intrinsic to Himself, nor can they take from Him anything of His own. In other words, He cannot receive that inner mutation which is philosophically called passio, and which in its general meaning denotes a change made in a substance by the action of some being.

This being premised as the basis of the following dissertation, let us consider any finite substance: and since it is easier to descend from the more perfect to the less, when the more perfect is known to us, we shall begin with man. Now by mentally abstracting from man all action, all passion, every faculty, what remains of him The bare essence of the human individual, as constituted by the soul substantially informing the corporeal matter. Whatever therefore we may conceive as happening to him when thus constituted and determined, will not be a substantial form that determines his nature, but an accidental form, which adds nothing more than quality. Therefore, remembering that besides human nature with its natural faculties, man has dispositions that adorn it and make it fitter for action, we must acknowledge that these are true qualities.

When a man acts either with his intellect or with his will, or with any other power that he has, there certainly happens to him a modification that before was not; and this is a quality. And, when at the sight of an object, pleasing or otherwise, he receives in his senses and in his soul an impression that was not there before, this, too, is a quality. Lastly, the human soul, as the substantial form, is the determining principle of the substances that nourish man to become part of his nature; and thus it gives in various ways to the body a certain extension, quantity and figure. Here again there is quality. We can therefore distinguish four species of quality, of which the first belongs to Being; the second to action; the third to passion; the fourth to quantity. "Properly speaking," says St. Thomas, "quality means a certain mode of substance. . . . Now the mode, or the determination of the subject, according to accidental Being, may be understood either according to the nature of the subject, or in reference to action, or to passion, (these proceed from the principles of nature which are matter and form,) or according to quantity. If we take the mode or determination of the subject according to quantity, we have the fourth species of quality. . . . The mode or determination of the subject according to action and passion gives the second and third species of quality. . . . But the mode or determination of the subject according to the nature of the thing belongs to the first species of quality.{1} . . . This does not contradict what he lays down in his commentary on the Sentences, where he says that the compositum does not operate in virtue of the matter, but of the form, which is its actus and principle of action. "The quantity," he says, "belongs to matter, the quality to Form."{2} For it is not affirmed that the said species of quality is quantity itself. It is the determination that is in the composite being under this or that quantity; and though the quantity belongs to matter, the determination is by virtue of the form.

Of the species inferior to man, whether they have life or have not, we must consider firstly their substantial being: secondly, what is accidental in them, constituted by the four different species of quality before mentioned. If an atom of oxygen, for instance, receives into itself a disposition which it previously had not, it will have a quality of the first species: and being in fact able to operate on another by attracting or altering, it will have a modification that contains the quality of the second species. If instead of that, it receives into itself the operation of another, it will acquire through the change undergone a quality of the third species. Lastly, if by virtue of an extrinsic cause, its proper quantity comes to be so determined that it acquires a different conformation of parts, that quality will belong to the fourth species.

We must observe that all the corporeal substances of equal matter have substantial forms, which, though differing from each other in perfection, have something in common, as we have seen by the comparison that Aristotle and St. Thomas took from geometrical figures and numbers. As in every polygon there is the triangle, and in every number there is unity, so in every substantial form there is an inferior or elementary form, not formally but virtually. This applies to qualities also, which, as we have said, are in being by reason of form. Hence the lowest qualities of the lowest elementary substance are common to all the superior substances. Thus, for instance, we find that attraction and gravitation, subjection to heat, expansion and the rest, are common to all corporeal substances. Since then a more perfect being has a substantial form that contains the perfections of the inferior forms, it must also possess their qualities. But as in a one being all must be in harmony and order, so even in the qualities, there is a certain law by which, where the inferior qualities would clash with the superior, the inferior are there in a remitted degree, or, in modern language, diminished or neutralized. "We must hold with the philosopher (Aristotle)," says St. Thomas, "that the forms of the elements remain in the mixture, not actually, but virtually. The qualities of the elements properly remain, though remitted; and in them appears the virtue of the elementary forms."{3}

And now, to make the whole theory of the system clear as to the gradation in the modes operating and the qualities of all beings, we cannot do better than quote another grand passage from the Angelic Doctor, where he reduces it to order and unity, giving us a sure foundation of rational physics.

"There is nothing," he says, "that more immediately and intimately belongs to things than Being; and therefore, since matter is actuated by form, the form that gives being to the matter must be conceived as coming to it first of all things, and most intimately Now it is a property of the substantial form that it gives being absolutely to matter; FOR THE SUBSTANTIAL FORM IS THAT BY WHICH A THING IS WHAT IT IS. The accidental forms do not give being absolutely, but in one respect, such as being great, or coloured, etc. Hence, if there is a form that does not give being to matter absolutely, but comes to matter already actuated by some form, it will not be substantial. Hence it is evident that between substantial form and matter there cannot be any intermediate substantial form (as some will have it) supposing that, according to the order of genera, of which one is under the other, there is an order of diverse forms in matter: as, for instance, that matter has the being of actual substance from one form, the being of corporeal substance from another, the being of an animated body from another, and so on. But according to that position the first form only, by which the actual being of substance was given, would be substantial. All the others would be accidental; for the substantial form, as we have already said, is that which constitutes the determinate being, (quae facit hoc aliquid.) We must therefore say that one and the same form is that by which a thing is a determinate substance and by which it is determined in its ultimate species (specialissima), and in all the intermediate genera," (by which, for example, a man is a man and an animal and a living creature and a corporeal substance).

Consequently, since the forms of natural things are like numbers, in which the addition and subtraction of a unit makes a different species, we must understand that the diversity of natural forms, according to which the matter is constituted in different species, is because one form adds a greater perfection. For instance, one form constitutes a substance in corporeal being only. . . . Another and more perfect form constitutes matter in vital as well as in corporeal being. And then another form gives to it not only corporeal and vital being, but also sensitive being, and so forth. We must see therefore that the more perfect form, inasmuch as simultaneously with the matter it constitutes the compositum in the perfection of an inferior grade, must be understood as material with respect to an ulterior perfection, and so on. Thus materia prima, as constituted in corporeal being, is matter with respect to the ulterior perfection of that which has life. Hence (logically) the body is the genus of the living body, and its being animated or living is the differentia. For the genus is as the matter, the differentia is as the form; and thus in a manner one and the same form, as actuating matter in a lower grade, is midway between the matter and itself as actuating it in a higher grade. Matter understood as constituted in substantial being according to the perfection of an inferior grade, must consequently be supposed as subject to accidents. For a substance in that lower grade of perfection must have certain accidents proper to itself."

"Thus, when we say that man is a corporeal substance, living, sensitive and rational, we do not mean that he is constituted in these diverse grades by diverse forms. We mean that the perfect form, the soul, which makes him rational, makes him a sensitive substance also, and a living substance and a corporeal substance; for since every superior grade presupposes the inferior, the human soul as constituting the rational grade, presupposes itself as constituting the sensitive grade, or sensitive being (esse) with its accidents and qualities and so on."

St. Thomas goes on to say: "Since then the soul is the substantial form, as constituting man in a determinate species of substance, there is no substantial form between the soul and materia prima: but man is perfected by his rational soul according to the different degrees of perfection, so as to be a body and an animated body and a rational animal. But matter, understood as receiving from the rational soul the perfections of a lower grade -- suppose it to be a body and an animated body and an animal -- must be understood as suitably disposed for the rational soul that gives the ultimate perfection. Thus the soul, as the form that gives being, has nothing between itself and materia prima. Now, since the same form that gives being to matter is also the principle of operation, and because everything acts according to what it actually is, the soul like every other form must be a principle of operation. But we must consider that according to the grades of the forms with respect to the perfection of Being, there is also a grade in their virtue of operating, because that which operates has already an actual existence. Therefore, the more perfect a form is in giving being, the greater is its virtue in operating; and the more perfect forms operate more and with greater diversity than the less perfect. Hence it is that in the less perfect things diversity of accidents is sufficient for diversity of operation, while the more perfect require diversity of parts also, more or less, according to the perfection of the form. Thus we see that fire operates in diverse ways according to the diversity of accidents, such as rising by reason of its lightness, warming by its heat, and so on: yet each of these operations belongs to the fire as a whole. But in animated bodies, which have nobler forms, different parts are assigned for different operations, as in plants the operation of the root is different from that of the boughs or of the trunk; and the more perfect an animated body is, the more does it require, by reason of its greater perfection, a greater diversity in its parts. Therefore, since the rational soul is the most perfect of natural forms, in man do we find the greatest distinction of parts owing to the diversity of his operations; and the soul gives to each of them substantial being in the manner that is suitable to its operations. This is marked by the fact that, when the soul is separated, the flesh or the eye remains only equivoce. Now, since the order of instruments must accord with the order of the operations, and, of the diverse operations that are from the soul, one naturally precedes another, so one part of the body must be moved by another to do its own work. Thus then, between the soul as the mover and the principle of operation, and the whole body, there is some medium; for by means of some part first moved it moves the other parts to their work, as by means of the heart it moves the other members to their vital operations. But when it gives being to the body, it immediately gives to every part substantial and specific being. And this is why many people say that the soul, as being the form of the body, is united to the body without a medium, but, as being the mover of the body, is united thereto through a medium: which accords with the opinion of Aristotle, who affirms the soul to be the substantial form of the body. But some people, supposing with Plato that the soul is united to the body as one substance to another substance" (that is, one complete substance not resulting therefrom), "had to suppose media through which the soul could be united to the body, because diverse and distant substances are not united unless there is something to unite them. And so some of them supposed that a fluid or humour is the medium between the soul and the body, while some supposed it to be light, and others believed it to be the powers of the soul, or something of the sort.{4} But none of these things are necessary, if the soul is the form of the body. For a thing, whatever it may be, is one because it is an ens, and therefore, since the form by itself gives being to matter, by itself is it united to materia prima, and not by anything else."{5}

Here ends our long quotation from the Angelic Doctor. It went beyond the question before us by speaking of animated beings and of human beings; but that is not altogether out of place, as we shall see further on.

And now, having discoursed on the mutual operation of the corporeal substances, according to the perfection of their being, we have to see how this can happen between substances far apart. These, as St. Thomas says, must approach in order to operate. "Alteration," he says, cannot happen without a previous change of place; for in order that the alteration may take place, the alterant must be nearer than before to the altered."{6} And since this approach may be either by internal attraction or by external impulse, we had better speak of the former as being more difficult.

{1} Summa, 1a. 2ae. Q. xlix. 2.

{2} Bk. xii. iv. Q. 1.

{3} Summa, P. i. Q. lxxvi. a. 4 ad 4.

{4} And all they who suppose that the soul is united to the body by means of the biotic fluid, or by ether, or by physical influx, fall into this error.

{5} De anima, art. 9.

{6} Contra Gent., iii. 82.

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