Page 29 of 48

We have thus discovered that all motions conspire together, or form a system. But in their unity they do not cease to be motions, or variously differentiated members. Through this differentiation, or mutual reaction of motions, there comes about the appearance of boundaries, of separation. From these boundaries or terminations arise the form and size of bodies. From motion also proceeds the cohesion of bodies, in the sense that each relative system resists dissolution, or hangs together. Says Leibniz, "The motions, since they are conspiring, would be troubled by separation; and accordingly this can be accomplished only by violence and with resistance." Not only form, size, and stability depend upon motion, but also the sensible, the "secondary" qualities. "It must not be supposed that color, pain, sound, etc., are arbitrary and without relation to their causes. It is not God's way to act with so little reason and order. There is a kind of resemblance, not entire, but of relation, of order. We say, for example, 'Light is in the fire,' since there are motions in the fire which are imperceptible in their separation, but which are sensible in their conjunction or confusion; and this is what is made known in the idea of light." In other words, color, sound, etc., even pain, are still the perception of motion, but in a confused way. We thus see how thoroughly Leibniz carries back all the properties of bodies to motion. To sum up, motion is the origin of the relative solidity, the divisibleness, the form, the size, the cohesion, or active resistance of bodies, and of their properties as made known to us in immediate sensation.

In all that has been said it has been implied that extension is already in existence; "first matter" is supposed to fill all space, and motion to determine it to take upon itself its actual concrete properties. But this "first matter," when thus spoken of, has a somewhat mythological sound, even if it be admitted that it is an abstraction. For how can an abstraction be extended in space, and how can it form, as it were, a background upon which motion displays itself? The idea of "first matter" in its relation to extension evidently demands explanation. In seeking this explanation we shall also learn about that "subject" which Leibniz said was necessarily presupposed in extension, as a concrete thing is required for a quality.

The clew to the view of Leibniz upon this point may be derived, I think, from the following quotations:—

"If it were possible to see what makes extension, that kind of extension which falls under our eyes at present would vanish, and our minds would perceive nothing else than simple realities existing in mutual externality to one another. It would be as if we could distinguish the minute particles of matter variously disposed from which a painted image is formed: if we could do it, the image, which is nothing but a phenomenon, would vanish. . . . If we think of two simple realities as both existing at the same time, but distinct from one another, we look at them as if they were outside of one another, and hence conceive them as extended."

The monads are outside of one another, not spatially, but ideally; but this reciprocal distinction from one another, if it is to appear in phenomenal mode, must take the form of an image, and the image is spatial. But if the monads were pure activity, they would not take phenomenal form or appear in an image. They would always be thought just as they are,—unextended activities realizing the spiritual essence of the universe. But they are not pure activity; they are passive as well. It is in virtue of this passive element that the ideal externality takes upon itself phenomenal or sensible form, and thus appears as spatial externality.

Leibniz, in a passage already quoted, refers to the diffusion of materiality or antitypia. This word, which is of frequent occurrence in the discussions of Leibniz, he translates generally as "impenetrability," sometimes as "passive resistance." It corresponds to the solidity or resistance of which Locke spoke as forming the essence of matter. Antitypia is the representation by a monad of the passive element in other monads. Leibniz sometimes speaks as if all created monads had in themselves antitypia, and hence extension; but he more accurately expresses it by saying that they need (exigent) it. This is a technical term which he elsewhere uses to express the relation of the possible to the actual. The possible "needs" the actual, not in the sense that it necessarily requires existence, but in the sense that when the actual gives it existence, it is the logical basis of the actual,—the actual, on the other hand, being its real complement. The passivity of the monad is therefore at once the logical basis and the possibility of the impenetrability of matter. It is owing to the passivity of the monad that it does not adequately reflect (that it is not transparent to, so to speak) the activities of other monads. In its irresponsiveness, it fails to mirror them in itself. It may be said, therefore, to be impenetrable to them. They in turn, so far as they are passive, are impenetrable to it. Now the impenetrable is, ex vi terminis, that which excludes, and that which excludes, not in virtue of its active elasticity, but in virtue of its mere inertia, its dead weight, as it were, of resistance. But mutual exclusion of this passive sort constitutes that which is extended. Extension is the abstract quality of this concrete subject. Such, in effect, is the deduction which Leibniz gives of body, or physical matter, from matter as metaphysical; of matter as sensible or phenomenal, from matter as ideal or as intelligible.

If we put together what has been said, it is clear that material phenomena (bodies, corpora, in Leibniz's phrase) simply repeat in another sphere the properties of the spiritual monad. There is a complete parallelism between every property, each to each, and this necessarily; for every property of "body" is in logical dependence upon, and a phenomenalization of, some spiritual or ideal quality. Motion is the source of all the dynamic qualities of body, and motion is the reflection of Force, that force which is Life. But this force in all finite forms is conditioned by a passive, unreceptive, unresponsive factor; and this must also have its correlate in "body." This correlate is primarily impenetrability, and secondarily extension. Thus it is that concrete body always manifests motion, indeed, but upon a background of extension, and against inertia. It never has free play; had it an unrestrained field of activity, extension would disappear, and spatial motion would vanish into ideal energy. On the other hand, were the essence of matter found in resistance or impenetrability, it would be wholly inert; it would be a monotone of extension, without variety of form or cohesion. As Leibniz puts it with reference to Locke, "body" implies motion, or impetuosity, resistance, and cohesion. Motion is the active principle, resistance the passive; while cohesion, with its various grades of completeness, which produce form, size, and solidity, is the result of their union.

Leibniz, like Plato, has an intermediary between the rational and the sensible; and as Plato found that it was mathematical relations that mediate between the permanent and unified Ideas and the changing manifold objects, so Leibniz found that the relations of space and time form the natural transition from the sphere of monads to the world of bodies. As Plato found that it was the possibility of applying mathematical considerations to the world of images that showed the participation of Ideas in them, and constituted such reality as they had, so Leibniz found that space and time formed the element of order and regularity among sense phenomena, and thus brought them into kinship with the monads and made them subjects of science. It is implied in what is here said that Leibniz distinguished between space and time on the one hand, and duration and extension on the other. This distinction, which Leibniz draws repeatedly and with great care, has been generally overlooked by his commentators. But it is evident that this leaves Leibniz in a bad plight. Mathematics, in its various forms, is the science of spatial and temporal relations. But if these are identical with the forms of duration and extension, they are purely phenomenal and sensible. The science of them, according to the Leibnizian distinction between the absolutely real and the phenomenally real, would be then a science of the confused, the imperfect, and the transitory; in fact, no science at all. But mathematics, on the contrary, is to Leibniz the type of demonstrative, conclusive science. Space and time are, in his own words, "innate ideas," and the entire science of them is the drawing out of the content of these innate—that is, rational, distinct, and eternal—ideas. But extension and duration are sensible experiences; not rational, but phenomenal; not distinct, but confused; not eternal, but evanescent. We may be sure that this contradiction would not escape Leibniz, although it has many of his critics and historians.