The relation between primitive and derivative forces may be the hardest problem about the relation between Leibniz's physics and his metaphysics. He holds that derivative forces are modifications of primitive forces, but also that physical forces, which he classifies as derivative forces, belong to bodies, which are aggregates, whereas primitive forces belong to unextended perceiving substances (monads) and constitute their essence. This chapter addresses this problem, arguing that a major part of it can be solved on the supposition that physical events are only phenomena, and hence ultimately determined by modifications of the primitive forces of perceiving substances (monads).
Keywords: aggregates, derivative forces, Leibniz, metaphysics, modifications, monads, perceiving substances, phenomena, physical forces, physics, primitive forces