(1) that Leibnitz is really asking what space-occupation means, not how it is produced, (2) that body is not made up of substances at all, and therefore not of forces, (3) that a substance as a spiritual unity cannot occupy space. Accordingly, Leibnitz’s explanation of resistance has been entirely misunderstood. It is supposed that resistance is the activity by which a body repels all other bodies and maintains its own place. But this makes resistance not a passive but an active force; in other words, a mode of motion. Leibnitz, on the other hand, contends that there are two distinct forces–an active force, which is expressed as motion, and a passive force, which does not involve motion. This passive force or materia nuda is simply the limit to activity which is implied in the very nature of a finite being. Hence the resistance of a body is not a form of activity, a reaction, but the passivity or inertia bound up with the nature of the finite monad. Accordingly, the dynamical law, that as the mass increases the velocity diminishes, just means that in proportion to the degree of passivity or “matter” the greater is the inertia. It need hardly be added that impenetrability is another form of the same law.
Dillmann finds that Leibnitz’s conception of the representative character of monads has also been misunderstood. (1) Fischer’s view, that the monad represents the world in the same way as a torso represents a statue, finds no support in Leibnitz. (2) Nor can Zeller’s view, that the monad has an idea or image of the world, be accepted; for this assumes an independently existing world to which the monad is in no relation. The true view is that the world is actually present in each monad, but present from the point of view of its own limited activity. Each substance is a representation of its own body and movements, and through these of the external material world and its changes. The world so present, however, is phenomenal; it is not a mere idea-representation of an independently existing world, but the presentation in a single spiritual being of what it is itself in its inner nature. This phenomenal world is thus the means of sensualizing the inner activity of the monad, and hence the most abstract thought must present itself in the form of an image.
So far it has been shown that the mechanical conception of the world, when taken as absolute, leads to insuperable difficulties, which can be got rid of only if we regard it as the form in which real substantial unities express their inner nature. Every monad is a primitive force or unity, which is continually realizing itself in an active or moving force, but realizing itself only in the limited way possible