  Kant's Physical Monadology (1756) takes as its task the reconciliation of the infinite divisibility of space, as maintained in geometry, with the simplicity of substances, which Kant believes is required in metaphysics. As was the case with his earlier works, the essential feature of his reconciliation lies in the way in which his matter theory is supported by his metaphysical views. Specifically, Kant asserts that simple substances fill space not by means of their mere existence, but rather in virtue of their spheres of activity. As a result, any division of the relevant spheres of activity does not compromise the simplicity of the substances themselves, since the spatial properties of substances (including the infinite divisibility of space) arise from the interaction between their activities rather than from their intrinsic features. In the course of the Physical Monadology, Kant also argues for the necessity of attractive and repulsive forces and attributes a significant role to the force of inertia. Kant's acceptance of such Newtonian principles represents an important change of position over the True Estimation, where Kant rejects the principle of inertia and pursues a dynamical theory much more in line with Leibniz's views.