Excerpts from Robert Nozick's "Invariances" Necessary truths are invariant across all possible worlds, contingent ones across only some.

Identities formed with proper names may be contingent. this claim is made first through an example. the paper then develops a theory of the semantics of concrete things, with contingent identity as a consequence. this general theory lets concrete things be made up canonically from fundamental physical entities. it includes theories of proper names, variables, cross-world identity with respect to a sortal, and modal and dispositional properties. the theory, it is argued, is coherent and superior to its rivals, in that (...) it stems naturally from a systematic picture of the physical world. (shrink)

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)

The objects we encounter in ordinary life and scientific practice - cars, trees, people, houses, molecules, galaxies, and the like - have long been a fruitful source of perplexity for metaphysicians. The Structure of Objects gives an original analysis of those material objects to which we take ourselves to be committed in our ordinary, scientifically informed discourse. Koslicki focuses on material objects in particular, or, as metaphysicians like to call them "concrete particulars", i.e., objects which occupy a single region of (...) space-time at each time at which they exist and which have a certain range of properties that go along with space-occupancy, such as weight, shape, color, texture, and temperature. The Structure of Objects focuses in particular on the question of how the parts of such objects, assuming that they have parts, are related to the wholes which they compose. (shrink)

The thesis is divided into three chapters. The first chapter considers how we ought to understand a thesis of contingent identity if it is to accomplish the work it is proposed to accomplish while at the same time avoiding certain obvious and otherwise persuasive objections. ;I begin by presenting a metaphysical thesis I call the Thesis of Contingent Identity, and defending it against alternatives. I then set out the principal objection to the Thesis, the objection from modal properties, and offer (...) a response. The chapter concludes with an appendix devoted to criticizing Allan Gibbard's and H. W. Noonan's accounts of contingent identity and their relpies to the objection from modal properties. The chief weakness in their proposals is that they concentrate on the semantical while neglecting the central metaphysical issues of contingent identity. In the process, they compromise the metaphysics they had intended to defend. ;The second chapter contains a discussion of some of the technical issues surrounding the Thesis of Contingent Identity. A robust version of the semantics outlined in the first chapter is presented and contrasted with competing alternatives. It has been said that semantic considerations alone cannot decide against contingent identity; I show why this is so. The chapter ends by considering in what sense the Thesis actually expresses contingent identity, and how it affects our views on which logic is the best modal logic for metaphysical necessity. ;The third chapter investigates and criticizes challenges to the Thesis of Contingent Identity from the transitivity of identity and the thesis that names are rigid designators. I argue that, according to the approach to contingent identity outlined in the previous chapters, the identity relation behaves normally. Claims that it violates transitivity are based on an equivocation which is exposed by paying careful attention to the notion of perspective . ;Similarly, I argue that the thesis that names are rigid designators is compatible with the Thesis of Contingent Identity. I review the debate between Kripke and Gibbard and criticize the weakness in the latter's approach. Moreover, I argue that close scrutiny of the influence and function of names uncovers an equivocation in certain arguments purporting to establish an incompatability between contingent identity and rigid designation. These considerations point to the hypothesis that some names might have multiple possible referents. The chapter concludes with some elaboration and defence of this hypothesis. (shrink)