Is There a Pre-Established Harmony of Aggregates in the Leibnizian Dynamics, or Do Non-Substantial Bodies Interact?

Is There a Pre-Established Harmony of Aggregates in the Leibnizian Dynamics, or Do Non-Substantial Bodies Interact? GREGORY BROWN AMONG STUDENTS OF HIS SYSTEM, the relationshipbetween Leibniz's dynamics and his metaphysics has long been a subject of intense interest and dispute. For Anglo-American scholars of this century, the early tone was set by Bertrand Russell's rather grim assessment "that the relation of Leibniz's Dynamics to his Metaphysics is hopelessly confused, and that the one cannot stand while the other is maintained. ''~ As Russell saw it, Leibniz's commitment to the noncommunication thesis--the metaphysical thesis that, strictly speaking, created substances are not capable of causal interaction'--could not be reconciled with the obvious demand, in the science of dynamics, to understand physical phenomena in terms of a genuine causal interaction among material particles: "Even when a thing is defined as one causal series," Russell argued, we can hardly escape the admission, which however is directly self-contradictory, that things do, after all, interact. And this is, in fact, admitted practically in Leibniz's writings. Although Dynamics requires us to assign causal action to each piece of matter, it requires us, just as much, to take account of all material particles in discussing what will happen to any one. That is, we require, on a purely dynamical basis, to admit transeunt action, the action of one thing on another. This was not avoided by Leibniz: on the contrary, the purely material Bertrand Russell, A Critical Exposition of the Philosophy of Leibniz, ~nd ed. (London: George Allen & Unwin, 1937), 89. ' Leibniz embraced this principle at a relatively early point in his career. For example, in a famous passage from the Discourse on Metaphysics (1686) he wrote that "each substance is as a world apart, independent of everything outside of itself except God" (G.IV.439 = L.312). [53] 54 JOURNAL OF THE HISTORY OF PHILOSOPHY 30:1 JANUARY 1992 world remained, for him, one in which every motion affects every other, though direct interaction occurs only in impact.3 In a recent article,4 Richard Miller has attempted to rebut Russell's charge against Leibniz by arguing that while Leibniz did indeed recognize a kind of genuine interaction among the aggregates of substances that form the material bodies discussed in dynamics, this does not imply any inconsistency with the metaphysical thesis of non-communication; and the reason no inconsistency is implied, according to Miller, is simply that the non-communication thesis is not properly transferable from substances to the aggregates of these that comprise the material bodies discussed in dynamics. In the second part of this paper, I formulate a general argument against Miller's position and provide some textual evidence that Leibniz did in fact regard the non-communication thesis as holding for aggregates as well as for substances; I also offer an alternative to Miller's way of responding to the charge of inconsistency that Russell brought against Leibniz. I take it to be an important moral of the story I shall tell that great care must be exercised in determining how to move, and how tojustify the moves one makes, between the levels of Leibniz's system. Thus to further motivate my discussion, I want briefly to consider, in the first part of my paper, how some other commentators, and even Leibniz himself, have muddied the waters of interpretation by not exercising such care. 1. In his article on "Leibniz and the Foundations of Physics: The Middle Years," Daniel Garber has argued that for some considerable time (during most of the period of the 168os and '9os) Leibniz was committed to the view that the fundamental, metaphysical units were not unextended monads, as in his most mature period, but something more straightforwardly Aristotelian in nature, namely, corporeal substances. These substances are concreta of form, or primitive active force, and matter, or primitive passive force; they, as well as mere aggregates of them, are also subjects of derivative forces, which are limitations , or modes, of primitive forces. They, as well as mere aggregates of them, are also spatially extended. Garber's interpretation of the metaphysics of Leibniz 's middle years is, I think, sufficientlywell known that...