There is a well-known argument from Leibniz's Law for the view that coincident material things may be distinct. For given that they differ in their properties, then how can they be the same? However, many philosophers have suggested that this apparent difference in properties is the product of a linguistic illusion; there is just one thing out there, but different sorts or guises under which it may be described. I attempt to show that this ‘opacity’ defence has intolerable consequences for (...) the functioning of our language and that the original argument should therefore be allowed to stand. (shrink)

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I defend my paper ‘The Non-identity of a Material Thing and Its Matter’ against objections from Bryan Frances and Jeffrey King.

A lot of people believe that distinct objects can occupy precisely the same place for the entire time during which they exist. Such people have to provide an answer to the 'grounding problem' – they have to explain how such things, alike in so many ways, nonetheless manage to fall under different sortals, or have different modal properties. I argue in detail that they cannot say that there is anything in virtue of which spatio-temporally coincident things have those properties. However, (...) I also argue that this may not be as bad as it looks, and that there is a way to make sense of the claim that such properties are primitive. (shrink)

The existence and importance of supervenience principles for identity across times and worlds have been noted, but insufficient attention has been paid to their precise nature. Such attention is repaid with philosophical dividends. The issues in the formulation of the supervenience principles are two. The first involves the relevant variety of supervenience: that variety is global, but there are in fact two versions of global supervenience that must be distinguished. The second involves the subject matter: the names “identity over time” (...) and “identity across worlds” are misnomers, for in neither case is identity at issue. The philosophical dividends then follow. Nathan Salmon’s argument that identity over time needs no “grounds” in matters of qualitative fact can be answered, as can an argument offered by many, that coincident objects would require objectionably ungrounded differences in identities across times and worlds. (shrink)

How can a statue and a piece of alloy be coincident at any time at which they exist and yet differ in their modal properties? I argue that this question demands an answer and that the only plausible answer is one that posits a difference in the form of the two objects.

It is argued that there are three main forms of necessity --the metaphysical, the natural and the normative--and that none of them is reducible to the others or to any other form of necessity. In arguing for a distinctive form of natural necessity, it is necessary to refute a version of the doctrine of scientific essentialism; and in arguing for a distinctive form of normative necessity, it is necessary to refute certain traditional and contemporary versions of ethical naturalism.

It is often said that the same particles can simultaneously make up two or more material objects that differ in kind and in their mental, biological, and other qualitative properties. Others wonder how objects made of the same parts in the same arrangement and surroundings could differ in these ways. I clarify this worry and show that attempts to dismiss or solve it miss its point. At most one can argue that it is a problem we can live with.

I compare a Lewisian defence of monism with Kit Fine's defence of pluralism. I argue that the Lewisian defence is, at present, the clearer in its explanatory intent and ontological commitments. I challenge Fine to explain more fully the nature of the entities that he postulates and the relationship between continuous material objects and the parts of those rigid embodiments in terms of which he proposes to explain crucial, modal and sortal, features of those objects.

Locke’s thesis states that no two things of the same sort can be in the same place at the same time. The thesis has recently received extensive discussion, with some philosophers attempting to find arguments in its favour and others attempting to provide counter-examples. However, neither the arguments nor the counter-examples have been especially convincing; and it is my aim, in this short note, to present what I believe is a more convincing counter-example to the thesis.

I aim to show that there are cases in which an ordinary material object exists intermittently. Afterwards there are a few words about the consequences of acknowledging such cases, but what is of more interest is the route by which the conclusion is reached. When deciding among competing descriptions of the cases considered, I have tried to reduce to a minimum the role of intuitive judgment, and I have based several arguments on "metaphysical principles," two of which I have defended.

Co-location is compatible with the doctrine of microphysical supervenience. Microphysical supervenience involves intrinsic qualitative properties that supervene on microphysical structures. Two different objects, such as Socrates and the lump of tissue of which he is constituted, can be co-located objects that supervene on different sets of properties. Some of the properties are shared, but others, such as the human-determining properties or the lump-determining properties, supervene only on one object or the other. Therefore, properties at the same location can be arranged (...) so as to constitute more than one object at the same time. (shrink)