XIII.
MECHANICAL INERTIA AND PHYSICAL ACTIVITY OF BODIES.
IN its primary signification inertia means want of art, and in that sense a thing that operates without art would be called inert. But afterwards it was extended to mean inactivity or even laziness. Lustremus animo has artes, says Cicero, quibus qui carebant inertes nominabantur. Postea tamen consuetudo obtinuit, ut pro ignavo potius et deside accipiatur.{1} Lastly it was employed to mean the want of an inner principle of activity. And in this sense bodies are called inert. The question of whether they are so, or not, is differently solved, and, according to the solution of it, men philosophize variously about corporeal things.
The followers of the Mechanic system say that bodies have no principle of physical activity, and reduce all natural phenomena to shocks mutually given and received by atoms. Hence their principle: "There is nothing in nature but matter and motion: and motion proceeds from motion alone." Some of the Dynamic school come near to this opinion: which at first sight seems very strange and contradictory. But they soften it off in a way, assigning to all corporeal beings not an intrinsic, but an extrinsic inertness: and so they say that forces per se subsisting can operate on themselves, but not reciprocally, because they are distant from each other. Hence they fall back on pre-established harmony or occasionalism, laying down that two forces show a mutual operation because they are inly determined by God to operate, or because God alone operates in both. Others admit action in distans and reciprocal activity of forces. All these hypotheses are in contradiction to the Physical system.
The Physical system acknowledges mechanical inertness, as common to all corporeal substances without life, and physical activity as common to them all in different ways. And in the first place, when we speak of mechanical inertia, we must understand it to mean that a body is capable of passing, by extrinsic impulse, from rest into motion, and incapable of changing by itself either the direction or the velocity of the motion. Both reason and experience will show that bodies are of themselves moveable, not requiring to occupy this or that portion of space more than another, and therefore that, when there is space and a cause able to give a suitable impulse, there is no sufficient reason why a body should not leave the place where it was. If the body is an atom, it cannot operate on itself, because immanent action is not proper to it, but only transient action, inasmuch as it acts on other bodies, but not on itself. Not operating on itself, it cannot free itself, so to speak, from the impulse received, nor increase it, nor change its direction. Reason then demonstrates mechanical inertia: and experience is continually proving that, when there are no impediments nor attraction and no repulsion of other bodies, an inanimate body goes by the impulse received, without ever changing its direction or otherwise modifying its motion.
But if bodies are mechanically inert, they are not physically so. Why, as the Angelic Doctor says, may we not allow all created substances to have a true physical efficiency and causality? To suppose that we may not would never occur to anyone capable of contemplating God's Infinite Goodness. The creative fiat brought all things out of nothing, and God saw that they were good, as participating of His own Goodness. Now the Divine Goodness not only requires perfection of being, but tends also to diffuse itself, because bonum est diffusivum sui. Therefore, since God created all things good, He imparts to them not only Being, but also that property of Good which consists in diffusing itself by operation. Like St. Dionysius and St. Augustine, the holy Doctor teaches that the Divine Goodness was the Cause of all things. "For God willed," said St. Thomas, "to communicate to creatures, as much as possible, the perfection of His goodness. Now the Divine Goodness has a twofold perfection: firstly, in respect of Himself as eminently containing every perfection; secondly, in respect of His operating on things, inasmuch as He is their Cause. Wherefore, it accorded with the Divine Goodness that this double perfection should be communicated to creatures, so that every created thing should, by the Divine Goodness, be made not only to be good, but also to give being and goodness to others, as the sun by diffusion of its rays makes bodies not only illuminated but luminous.
He remarks moreover that the faculty of operating is a natural consequence of being; so that whenever God gives being to a thing, He must enable it naturally to be a cause by its own operation. "That which gives the principal thing to something," says St. Thomas, "gives to the same all things that are a consequence of it. . . . Now doing in actu is a consequence of being in actu; as is evident in God, Who is the Actus Purus and the first Cause of the being of all things. . . . If therefore He communicated His likeness to things by making them be, it follows that He communicated His likeness to them by enabling them to act, so that each creature should have its proper operation."{3}
And the holy Doctor shows that, if the true efficiency of creatures be denied, the order of the universe, with its beauty and perfection, disappears. "To take away order from created things," he says, "is to take away what is best in them; for the individual things are good in themselves; but all of them together are best because of the order of the Universe; for the whole is always better than the parts, and is the end for which they are. But if their power of acting be taken away, the mutual interchanging order of things is taken away also. In fact things different in their natures cannot be bound together in the unity of order unless some are acting and others acted upon. It is therefore wrong to say that things have not their proper operations."{4} Passing over many other reasons which he brings forward to prove a true efficiency in all corporeal substances, we need only quote what he says in another part of the same chapter at the conclusion of an argument: "To deny, therefore," he says, "that created things have their proper operations, is to derogate from the Divine Goodness."{5}
But why should we look for philosophical arguments, when all nature speaks to us, persuades us, compels us to confess the truth about this? If we raise our eyes towards Heaven, we find it in the gravitation of the heavenly bodies and the marvellous laws of their revolutions. If we look on the earth, we have it in the fertilization of seeds, the formation of embryos, the increase of all living beings, the transformation of elements into compounds. If you acknowledge true activity, you can find your way in the labyrinth of your researches about light, heat, electricity, magnetism. Deny it, and you have to grope about without any guide at all. With the doctrine that acknowledges the efficiency of all secondary causes, that vary more or less by the rule of their comparative perfection, the whole universe becomes one harmonious chorus that sings the glories of its Maker. The contrary doctrine makes the universe mute. All is mystery -- not such a mystery as raises and sublimates the intellect of the believer, but a mystery that abases, depresses, destroys. We need not give other proofs here of such physical activity and efficiency in each of the substances. We shall only remark that, in this its fundamental doctrine, the Physical system agrees completely with the teaching of the Catholic Church. The greatest theologians have not hesitated to affirm that we cannot deny it without incurring the taint of rashness. "We must say," writes the great Suarez, "that created agents work, truly and properly, effects connatural and proportional to themselves. And I believe that this truth is not only most evident to sense and reason, but also most certain according to Catholic doctrine. Therefore, as for the former reason, St. Thomas called the contrary opinion foolish, so for the latter reason we may call it rash and erroneous, and, as such, deservedly rejected by all philosophers and theologians. . . Not immaterial substances only, but also material substances have a physical and true efficiency. This follows from the preceding doctrine with almost equal demonstration and certainty; for experience, reason and evidence speak as strongly in favour of natural and material causes as of immaterial causes."{6} And Ruvio says plainly that: Tollere efficientiam ab omnibus causis, vel etiam corporeis, error est non solum in fide catholica, sed in vera philosophia.{7} Cardinal Toledo speaks in like manner: Auferre efficientiam, he says, ab iis causis particularibus, nec est sacrae doctrinae, nec doctoribus sanctis, nec verae philosophiae consonum.{8} We are not bringing a theological doctrine to bear on our contradictors, for that in a philosophical treatise would not be allowable. But we have a right to say that those who would not reason on created things under the guidance of true philosophy destroyed science, and substituting their own wild imaginings, incurred the danger of that punishment with which God Himself has threatened them: Quoniam non intellexerunt opera Domini, et in opera manuum ejus, destrues illos, et non aedificabis eos.{9}
{1} III. de Fin.
{2} Quaest. Disp., Q. de Veritate, V. De Prov. 5.
{3} Contra Gent., iii. 69.
{4} Ibid.
{5} Ibid.
{6} Met. Disp., 15, Sect. I.
{7} In II. Phys., Tract. 2, Q. 2.
{8} In II. Phys., 3.
{9} Ps. xxvii. 5