to recognize that it is phenomenal, or presupposes a real substantial unity. But his meaning has been variously misunderstood. (1) Zeller supposes him to be arguing that body is composed of an infinity of indivisible, simple beings. But this is to confuse the monad with the atom. Leibnitz nowhere maintains that body may be analyzed into ultimate elements; he holds, on the contrary, that it has no ultimate elements, since every part of it is divided to infinity. The unity of body is therefore not in body itself, but in that which makes body possible. (2) Zeller also supposes Leibnitz to be dealing with the question of how we come to have the perception or apprehension of body. An infinity of individual substances are presupposed in body, but these can appear to us as a corporeal mass, only if we suppose a soul which combines those substances into a whole: body is therefore the confused idea of the relation subsisting between the soul and those substances. This is not the doctrine of Leibnitz: his view is that body is in itself a mere phenomenon, and therefore has no reality apart from soul.
Again, Leibnitz in his analysis of the idea of motion points out that motion conceived as mere change of place is purely relative, and hence he infers that it implies something permanent and unchangeable. This is very different from saying that it implies an underlying substrate. There is, in his view, no such substrate, but force is the unchangeable unity of substance, which manifests itself in time in the form of motion. Thus force is a name for the spiritual or quasi-spiritual unity containing in itself implicitly the totality of past, present, and future motions of a body. This capacity can, however, only be realized in so far as from moment to moment there is a tendency (nisus) to change of place. Now this tendency which is manifested outwardly as tendency to change of place is in the monad desire, i. e., the continuous effort after self-realization of all that is implied in its own unchangeable nature. The explanation of motion is therefore not to be found in the untenable hypothesis of an underlying substrate, which manifests itself in motion, but in the self-active realization of a spiritual unity.
As the current interpretation misconceives the Leibnitzian conception of motion, so it naturally misstates his views in regard to resistance and impenetrability. Starting from the false assumption that Leibnitz was asking in all cases how a certain phenomenon is produced by a thing-in-itself, his exponents have imagined him to affirm that a body occupies space because it is composed of forces. How preposterous this view is we may at once see if we consider