According to most contemporary philosophers, the Indiscernibility of Identicals is obviously true. We might therefore expect earlier philosophers to endorse it. But I will use a puzzle about identity over time to argue that Descartes would reject it.

Leibniz argues against Descartes’s conception of material substance based on considerations of unity. I examine a key premise of Leibniz’s argument, what I call the Plurality Thesis—the claim that matter (i.e. extension alone) is a plurality of parts. More specifically, I engage an objection to the Plurality Thesis stemming from what I call Material Monism—the claim that the physical world is a single material substance. I argue that Leibniz can productively engage this objection based on his view that matter is (...) discrete. The discreteness of matter provides two aspects of support for the Plurality Thesis. First, it indicates that the parts of matter do not share boundaries and are, therefore, independent in an important sense. Second, it indicates that the parts of matter are determinate and are, therefore, ontologically prior to the wholes they compose. (shrink)

Descartes notoriously characterizes substance in two ways: first, as an ultimate subject of properties ; second, as an independent entity. The characterizations have appeared to many to diverge on the definition as well as the scope of the notion of substance. For it is often thought that the ultimate subject of properties need not—and, in some cases, cannot—be independent. Drawing on a suite of historical, textual, and philosophical considerations, this essay argues for an interpretation that reconciles Descartes's two characterizations. It (...) proposes that both characterizations invoke a type of independence that obtains just in case there is no relation to another entity that holds by the nature of the entity in question. Even though the ultimate subject of properties is sometimes not independent in other respects, it satisfies this independence-by-nature condition. (shrink)

Leibniz argues that Cartesian extension lacks the unity required to be a substance. A key premise of Leibniz’s argument is that matter is a collection or aggregation. I consider an objection to this premise raised by Leibniz’s correspondent Burchard de Volder and consider a variety of ways that Leibniz might be able to respond to De Volder’s objection. I argue that it is not easy for Leibniz to provide a dialectically relevant response and, further, that the difficulty arises from Leibniz’s (...) commitment to part-whole priority in the case of material wholes, a commitment not shared by De Volder. One major implication is that Leibniz relies on a bottom-up conception of material things, which makes his argument vulnerable to objections stemming from certain types of monist positions. (shrink)

It is a matter of continuing scholarly dispute whether Descartes offers a metaphysics of the material world that is “monist” or “pluralist.” One passage that has become crucial to this debate is from the Synopsis of the Meditations, in which Descartes argues that since “body taken in general” is a substance, and since all substances are “by their nature incorruptible,” this sort of body is incorruptible as well. In this article I defend a pluralist reading of this passage, according to (...) which there are indefinitely many bodies-taken-in-general, each of which counts as an incorruptible material substance. However, I also consider some surprising features of the argument in the Synopsis. One is that this argument conflicts with the implication in Descartes that any two “really distinct” substances can each exist without the other existing. Another is that the argument tends to undermine his suggestion that there is room at a fundamental metaphysical level for ordinary material objects. (shrink)

First, I offer a solution to the metaphysical problem of the mind–body relation, drawing on the fact of its distinctness in kind. Secondly, I demonstrate how, contrary to what is denied, Descartes’ metaphysical commitments allow for the intellect's clear and distinct conception of the mind–body union. Central to my two-fold defence is a novel account of the metaphysics of Descartes’ Causal Principle: its neutrality, and the unanalysable, fundamental nature of causality. Without the presupposition, and uniqueness of the mind-body union there (...) can be no mind-body interaction; this throws new light on current concerns in metaphysics and philosophy of mind. (shrink)