Massimo Mugnai’s Leibniz’s Theory of Relations is the only other book besides this one that is entirely about Leibniz’s views on relations and extrinsic denominations. The interpretation Mugnai develops is, in some respects, similar to the reductionist one espoused by Mates, Cover and Hawthorne, and others. For example, he claims that, for Leibniz, the only accidents to be found in substances are intrinsic, non-relational ones. Unlike most reductionists, however, he asserts that Leibniz allowed relational properties to be included in complete individual concepts. Mugnai, in opposition to what has come to be called the Russell- Couturat Thesis, thus believes that, for Leibniz, what is true at the level of individual concepts is not always true at the level of substances and their accidents. Mugnai also does not appear to accept the reductionist reading of NPE:

So, for Mugnai, NPE is the claim that

(M1), for all intents and purposes, is just (9) from chapter two. When Mugnai states in the above passage that NPE “must not be mistaken for the logical ontological assertion that every extrinsic relation or denomination is founded on specific qualities in the correlated objects,” I believe he means to distance himself from the standard reductionist reading of NPE. (M1) is clearly not the same understanding of NPE that reductionists endorse, nor is it the one I accept.