Moreover, whence does the passivity and whence does the inertia of [pg 676] matter proceed? Matter is passive, because its substantial term, whose reality entirely depends on actuation, is still actuable or potential with regard to accidental acts. Passivity is therefore nothing but the further actuability of the substantial term; whilst, on the contrary, matter is inert, because its substantial act and its substantial term are so related to one another that the motive power possessed by the former can never terminate its action to the latter; for this is the only reason why a material element cannot modify the determinations which it receives from without. Hence inertia is nothing but the result of the special relation intervening between the principle of activity and the principle of passivity in the constitution of material substance; or, in other terms, inertia is a corollary of the essential correlation of form and matter, and, therefore, is to be traced, not, as passivity, to the essential term of the substance, but to its essential complement. This shows that, in the phrase matter is inert, the word “matter” stands for the material substance itself, and not for the matter, or potential term, which is under the substantial form, and whose character is passivity.
The question we have here discussed may seem of very little importance; yet we had to give its solution, not only because the confusion of distinct notions is a source of difficulties and sophisms, but also because the given solution confirms the necessity of admitting the essential complement as the third principle of real being, and because in spiritual substances there is passivity, though not inertia; which shows how indispensable is our duty of distinguishing between the two.
From the preceding remarks we infer also that inertia belongs to the essence of material substance, not, however, as a constituent principle, but only as something implied in the nature of its constituent principles. As it is impossible to alter the nature of such principles without destroying the essence of matter, so also it is impossible for matter to cease to be inert so long as its essence remains unchanged. In a word, non-inert matter is a metaphysical impossibility.
Lastly, we may add that inertia does not admit of degrees; and therefore all material elements are equally inert. In fact, when we say that matter is inert, we mean, as has been explained, that material substance is entirely and absolutely incapable of imparting motion to itself. Now, absolute incapacity is perfect incapacity, and does not admit of degrees. Hence we may find in different bodies more or less of inert matter, but not more or less of inertia. This is true also of the passivity of matter; that is, we may find in different bodies more or less of passive matter, but not more or less of passivity; for passivity, as consisting in an absolute liability to accidental actuation, cannot admit of degrees.
A few conclusions.—It may be useful, and may prove satisfactory to our readers, to cast a glance over the ground we have trodden and the results so far reached. The sum and substance of the doctrine which we have endeavored to establish is contained in the following propositions:
I. Matter is not continuous, nor divisible in infinitum, nor has it any intrinsic quantity connected in any manner with its essential constitution.
II. All bodies are ultimately made up of primitive elements, physically simple and unextended, which being [pg 677] reached, the physical division of bodies cannot go further.
III. The primordial molecules, or so-called “atoms,” of all substances are so many systems of simple elements dynamically bound with one another by mutual action.
IV. The continuous extension, or geometric quantity, usually predicated of bodies, is the extension of the place comprised within the extreme limits of each body. It is, in other terms, the extension of the volume, not of the matter. Nevertheless, such an extension may be called “material,” not only because the terms of its dimensions are material, but also because in most bodies the elements and the molecules are so close that their action on our senses produces the appearance of material continuity.
V. The extension of bodies is real, though their material continuity is merely apparent; hence only the volumes of bodies, and not their masses, can be properly styled extended.