  The “bugs all the way down” model is not, however, the only model of fundamental metaphysics that one can find in Leibniz’s writings. In his most mature works, Leibniz suggests that at the deepest level of ontology, we find only simple, mind-like substances, or “monads.” Although strictly indivisible, Leibniz insists that monads can nonetheless be thought of as unities of form, insofar as they are active, and matter, insofar as they are passive. According to this metaphysics, the gross bodies studied by physicists are at least twice removed from monadic reality. Gross bodies are grounded in organisms, or “corporeal substances,” while corporeal substances are themselves grounded in simple substances, or “monads.” This same chain of ontological dependence, however, likewise holds for forces: the active forces attributed to gross bodies are “well-founded” in the active forces attributable to organisms, which are “well-founded” in the active forces of monads, just as the passive forces attributable to gross bodies are “well-founded” in the passive forces attributable to organisms, which in turn are “well-founded” in the passive forces of monads. A full understanding of these grounding relations would of course require a more detailed explication of the relations between monads, corporeal substances, and gross bodies, as well as a fuller account of what“grounding” amounts to in this context. Nonetheless, even this rough sketch should suffice to indicate the broad outlines of Leibniz’s commitment to founding the active and passive forces he postulates as part of his physics in the most fundamental level of reality which he postulates as part of his most mature metaphysics. 