This book is a defense of modal realism; the thesis that our world is but one of a plurality of worlds, and that the individuals that inhabit our world are only a few out of all the inhabitants of all the worlds. Lewis argues that the philosophical utility of modal realism is a good reason for believing that it is true.

Two things become one thing, something having parts, and something becoming something else, are cases of many things being identical with one thing. This apparent contradiction introduces others concerning transitivity of identity, discernibility of identicals, existence, and vague existence. I resolve the contradictions with a theory that identity, number, and existence are relative to standards for counting. What are many on some standard are one and the same on another. The theory gives an account of the discernibility of identicals using (...) phrases like “insofar as”. And it holds that standards for counting remain or shift depending on our purposes. (shrink)

Persistence through time is like extension through space. A road has spatial parts in the subregions of the region of space it occupies; likewise, an object that exists in time has temporal parts in the various subregions of the total region of time it occupies. This view — known variously as four dimensionalism, the doctrine of temporal parts, and the theory that objects “perdure” — is opposed to “three dimensionalism”, the doctrine that things “endure”, or are “wholly present”.1 I will (...) attempt to resolve this dispute in favor of four dimensionalism by means of a novel argument based on considerations of vagueness. But before argument in this area can be productive, I believe we must become much clearer than is customary about exactly what the dispute is, for the usual ways of formulating the dispute are flawed, especially where three dimensionalism is concerned. (shrink)

What is the relation between material objects and spacetime regions? Supposing that spacetime regions are one sort of substance, there remains the question of whether or not material objects are a second sort of substance. This is the question of dualistic versus monistic substantivalism. I will defend the monistic view. In particular, I will maintain that material objects should be identified with spacetime regions. There is the spacetime manifold, and the fundamental properties are pinned directly to it.

Paper begins: Chapter 4 of Hud Hudson’s stimulating book The metaphysics of hyperspace contains an discussion of the notion of location in a container spacetime. Hudson uses this idea to define a number of what we might call modes of extension or ways of being extended. A pertended object is what most people think of as a typical extended object — it is made up of spatial parts, one part for each region the object pervades. An entended object is an (...) extended simple (or a complex object made up of extended simples). Elsewhere, I’ve argued that entended objects are conceptually possible; that nothing about the concept of “extended” rules out entention. (More about how this argument works below). Hudson thinks that I did not go far enough. Besides pertended and entended objects, he also sees conceptual room for what he calls spanners and multiply located objects. These last two ways of being extended are even more exotic than extended simples. …. (shrink)

There’s an argument around from so-called “linguistic theories of vagueness”, plus some relatively uncontroversial considerations, to powerful metaphysical conclusions. David Lewis employs this argument to support the mereological principle of unrestricted composition, and Theodore Sider employs a similar argument not just for unrestricted composition but also for the doctrine of temporal parts. This sort of argument could be generalised, to produce a lot of other less palatable metaphysical conclusions. However, arguments to Lewis’s and Sider’s conclusions on the basis of considerations (...) about vagueness are uncompelling, even if we accept the crucial premises about vagueness. And a good thing too, since the generalised form of the argument would prove far too much. (shrink)

Entities of many kinds, not just material things, have been credited with parts. Armstrong , for example, has taken propositions and properties to be parts of their conjunctions, sets to be parts of sets that include them, and geographical regions and events to be parts of regions and events that contain them. The justification for bringing all these diverse relations under a single ‘part–whole’ concept is that they share all or most of the formal features articulated in mereology . But (...) the concept has also prompted an ontological thesis that has been expressed in various ways: that wholes are ‘no ontological addition’ to their parts ; that to list both a whole and its parts is ‘double counting’; and that there is ‘no more’ to a whole than its parts: for example, that there is no more to a conjunction than the conjuncts that are its parts, and whose truth or falsity determines whether it is true or false. For brevity, I shall express the thesis in the last of these ways, as the claim that entities with parts are ‘nothing but’ those parts. (shrink)

A solution to the problem of intrinsic change for enduring things should meet three conditions. It should not replace monadic intrinsic properties by relations. It should not replace the having simpliciter of properties by standing in some relation to them. It should not rely on an unexplained notion of having an intrinsic property at a time. Johnston's solution satisfies the first condition at the expense of the second. Haslanger's solution satisfies the first and second at the expense of the third.

is the second-order theory of the part-whole relation. It can express such hypotheses about the size of Reality as that there are inaccessibly many atoms. Take a non-empty class to have exactly its non-empty subclasses as parts; hence, its singleton subclasses as atomic parts. Then standard set theory becomes the theory of the member-singleton function—better, the theory of all singleton functions—within the framework of megethology. Given inaccessibly many atoms and a specification of which atoms are urelements, a singleton function exists, (...) unique up to isomorphism. (This article is partly abridged from my Parts of Classes, partly a sequel.). (shrink)

Ted Sider’s book makes a beautifully presented and compellingly argued case for four dimensionalism. Most of the arguments for four dimensionalism to be found in the literature seem to me to be uncompelling. Ted’s argument from vagueness, given in the last section of chapter 4, is a notable exception. After discussing that argument I will respond to his objections in section 5 chapter 5 to my own temporary identity view.

Sider has a favourable view of supersubstantivalism (the thesis that all material objects are identical to the regions of spacetime that they occupy). This paper argues that given supersubstantivalism, Sider's argument from vagueness for (mereological) universalism fails. I present Sider's vagueness argument (§§II-III), and explain why - given supersubstantivalism - some but not all regions must be concrete in order for the argument to work (§IV). Given this restriction on what regions can be concrete, I give a reductio of Sider's (...) argument (§V). I conclude with some brief comments on why this is not simply an ad hominem against Sider, and why this incompatibility of supersubstantivalism with the argument from vagueness is of broader interest (§VI). (shrink)

This essay interprets Butler’s distinction between identity in the loose and popular sense and in the strict and philosophical sense. Suppose there are different standards for counting the same things. Then what are two distinct things counting strictly may be one and the same thing counting loosely. Within a given standard identity is one-one. But across standards it is many-one. An alternative interpretation using the parts-whole relation fails, because that relation should be understood as many-one identity. Another alternative making identity (...) relative to sort fails, because whole and parts can be of the same sort. (shrink)

This book discusses a range of important issues in current philosophical work on the nature of possible worlds. Areas investigated include the theories of the nature of possible worlds, general questions about metaphysical analysis and questions about the direction of dependence between what is necessary or possible and what could be.

Some mereologists boast that their view of parts and wholes is ontologically innocent.[Lewis 1991: 72-87] They claim that a fusion is nothing over and above its parts; once you’ve committed to the parts, you get the fusion for free. In other words, fusions are not a further ontological commitment beyond the commitment to the parts. There are various proposals to explain how it is that fusions can come about so cheap. Perhaps the most straightforward of these explanations, and the one (...) I will be concerned with in this paper, is to accept the Strong Composition Thesis:2, 3.. (shrink)