This article argues that the Fourth and Fifth of John Toland's Letters to Serena are best understood as a creative confrontation of Spinoza and Leibniz ? one in which crucial aspects of Leibniz's thought are extracted from their original context and made to serve a purpose that is ultimately Spinozistic. Accordingly, it suggests that the critique of Spinoza that takes up so much of the fourth Letter, in particular, should be read as a means of `perfecting' Spinoza (via Leibniz), rather (...) than as the outright dismissal it might appear to be. In order to make its case, the article outlines: the supposed problems that Toland finds in Spinoza; what Toland takes from Leibniz, and what he discards, in order to solve these `problems'; and the imprint of Spinoza's naturalism on the eventual `solution' that Toland offers. The article concludes that, whatever the success of this `solution', Toland's speculative labours should still be treated as creative, perspicuous and intrinsically significant. (shrink)

The way Leibniz applied his philosophy to mathematics has been the subject of longstanding debates. A key piece of evidence is his letter to Masson on bodies. We offer an interpretation of this often misunderstood text, dealing with the status of infinite divisibility innature, rather than inmathematics. In line with this distinction, we offer a reading of the fictionality of infinitesimals. The letter has been claimed to support a reading of infinitesimals according to which they are logical fictions, contradictory in (...) their definition, and thus absolutely impossible. The advocates of such a reading have lumped infinitesimals with infinite wholes, which are rejected by Leibniz as contradicting the part–whole principle. Far from supporting this reading, the letter is arguably consistent with the view that infinitesimals, as inassignable quantities, arementis fictiones, i.e., (well-founded) fictions usable in mathematics, but possibly contrary to the Leibnizian principle of the harmony of things and not necessarily idealizing anything inrerum natura. Unlike infinite wholes, infinitesimals—as well as imaginary roots and other well-founded fictions—may involve accidental (as opposed to absolute) impossibilities, in accordance with the Leibnizian theories of knowledge and modality. (shrink)