There are two ways in which the Spinozistic world-view threatens to consume Leibniz's metaphysic. The first is necessitarianism, familiar both in tempting the early Leibniz and giving rise to an extended and difficult program of resistance from the late 1670s onward. The second threat, from Spinoza's one-substance doctrine, has received comparatively little attention. In chapter 5 of his A Critical Exposition of the Philosophy of Leibniz, Bertrand Russell makes the following, rather striking remark:

Russell's motivations for this remark are universally either ignored or under-appreciated. We propose to make a case for the Russellian verdict, and to offer an interpretive gloss on some rather cryptic Russellian remarks in the light of that case. In doing so, our overarching aim is to make manifest one of the deepest challenges facing the Leibnizian metaphysic, and moreover to bring into clearer relief a pressing concern for any metaphysics of individuals.

MOTIVATING THE ONE-SUBSTANCE THREAT

Famously, Leibniz declared that “Spinoza would be right, if there were no monads.” In the previous chapter we developed as best we could a picture of what monads are for Leibniz, namely, immanent active forms/laws from which accidents emanate. Leibniz's monadology tells us that there are many such immanent laws. A Spinozistic monadology would tell us that there is only one. Now that ontology is not exactly the threat we are concerned with here.