Chapter VIII.

       Material Phenomena and Their Reality.

       Table of Contents

      We have seen the necessity and nature of matter as deductions from the fundamental principles of Leibniz. We have seen that matter is a phenomenon or manifestation of spirit in an imperfect and confused way. But why should it appear as moving, as extended, as resisting, as having cohesion, with all the concrete qualities which always mark it? Is there any connection between these particular properties of matter as physical, and its “metaphysical” or ideal character? These are the questions which now occupy us. Stated more definitely, they take the following form: Is there any essential connection between the properties of matter as a metaphysical element, and its properties as a sensible fact of experience? Leibniz holds that there is. He does not, indeed, explicitly take the ground that we can deduce a priori all the characteristics of matter as a fact of actual experience from its rational notion, but he thinks we can find a certain analogy between the two, that the sensible qualities are images or reflexes of the spiritual qualities, witnessing, so far as possible, to their origin in pure energy.

      His position is as follows: that which in the monad is activity or substantial, is, in sensible matter, motion. That which in the monad is lack of a given activity, that which constitutes its subordinate position in the hierarchy of monads, is, in the sphere of material things, inertia. That which in the spiritual world is the individuality of monads, making each forever ideally distinct from every other, is, in the phenomenal realm, resistance or impenetrability. The perfect continuity of monads in the mundus intelligibilis has also its counterpart in the mundus sensibilis in the diffusion or extension of physical things.

      Instead of following out this analogy directly, it will rather be found convenient to take up Leibniz’s thought in its historical connection. We have already alluded to the fact that he began as a Cartesian, and that one of the first ideas which repelled him from that system of thought was the notion that the essence of matter is extension. His earliest philosophical writings, as he was gradually coming to the thoughts which thereafter dominated him, are upon this point. In general, his conclusions are as follows: If matter were extension, it would be incapable of passion or of action. Solidity, too, is a notion entirely opposed to the conception of mere extension. The idea of matter as extension contradicts some of the known laws of motion. It requires that the quantity of motion remain unchanged whenever two bodies come in contact, while as matter of fact it is the quantity of energy, that which the motion is capable of effecting, that remains unchanged; or, as he more often puts the objection, the Cartesian notion of matter requires that matter be wholly indifferent to motion, that there be nothing in it which resists motion when imparted. But, says Leibniz, there is something resisting, that to which Keppler gave the name “inertia.” It is not found to be true if one body impacts upon another that the second moves without diminishing the velocity or changing the direction of the first. On the other hand, just in proportion to the size of the second body, it resists and changes the motion of the first, up to the point of causing the first to rebound if small in comparison. And when it was replied that the retardation was due to the fact that the force moving the first body had now to be divided between two, Leibniz answered that this was simply to give up the contention, and besides the notion of extension to use that of force. If extension were the essence of matter, it should be possible to deduce all the properties of matter, or at least to account for them all, from it. But since, as just seen, this does not enable us to account for any of them, since for any of its concrete qualities we have to fall back on force, it is evident where the true essence of matter is to be found.

      Leibniz has another argument of a logical nature, as those already referred to are of a physical: “Those who claim that extension is a substance, reverse the order of words as well as of thoughts. Besides extension there must be a subject which is extended; that is to say, something to which it belongs to be repeated or continued. For extension is nothing but a repetition or continued multiplication of that which is spread out,—it is a plurality, a continuity, a co-existence of parts. Consequently, extension does not suffice to explain the nature of the repeated or manifold substance, of which the notion is anterior to that of its repetition.” Extension, in other words, is nothing substantial, it is not something which can exist by itself; it is only a quality, a property, a mode of being. It is always relative to something which has extension. As Leibniz says elsewhere: “I insist that extension is only an abstraction, and requires something which is extended. It presupposes some quality, some attribute, some nature in a subject which is extended, diffused, or continued. Extension is a diffusion of this quality. For example, in milk there is an extension or diffusion of whiteness; in the diamond an extension or diffusion of hardness; in body in general a diffusion of antitypia or materiality. There is accordingly in body something anterior to extension.”

      From the physical side, therefore, we find it impossible to account for the concrete properties of material phenomena from extension; on the logical we find that the idea of extension is always relative to that which is extended. What is that which is to be considered as the bearer of extension and the source of physical qualities? We are led back to the point at which we left the matter in the last chapter. It is force, and force both passive and active. Leibniz uses the term “matter” in at least three senses: it is the metaphysical element of passive force in the monad; it is the monad itself considered as, upon the whole, externally conditioned or unconscious; and it is the phenomenon resulting from the aggregation of the monads in the second sense. The first is naked matter, and is a pure abstraction; the second is the monad as material, as opposed to the monad, as soul; the third is clothed, or second matter, or, concretely, body, corpus. The first is unreal by itself; the second is one phase of substance; the third is not substantial, but is a reality, though a phenomenal one. It is from the substantial monad that we are to explain the two things now demanding explanation,—that element in bodies (matter in third sense) which is the source of their physical properties, and that which is the subject, the carrier, so to speak, of extension.

      That of which we are in search as the source of the physical qualities of bodies is motion. This is not force, but its “image.” It is force, says Leibniz, that “is the real element in motion; that is to say, it is that element which out of the present state induces a change in the future state.” As force, in other words, is the causal activity which effects the development of one “representation” of a monad out of another, so motion, in the realm of phenomena, is not only change, but change which is continuous and progressive, each new position being dependent upon the foregoing, and following out of it absolutely without break.

      Motion, therefore, is the manifestation of the ideal unity of substance,—a unity not of mere static inherence, but of a continuous process of activity. It is from this standpoint that Leibniz accounts for the so-called transference of motion from one body to another upon contact. The ordinary view of this, which looks at it as if one body loses the motion which another body gains, Leibniz ridicules, saying that those who hold this view seem to think that motion is a kind of thing, resembling, perchance, salt dissolved in water. The right view, on the other hand, does away with all appearance of mystery in the carrying over of motion from one body to another, for it recognizes that continuity is the very essence of motion, and that we do not have two things and a third process, but that the two bodies are phases or elements in one and the same system of movement.