- I borrow the title of this paper, slightly amended, from Parsons' recent 'Must a Four-Dimensionalist Believe in Temporal Parts?' Four-dimensionalism, as I use the term, is the view that persisting objects have four dimensions: they are four-dimensional 'worms' in space-time. This view is contrasted with three-dimensionalism, the view that persisting objects have three-dimensions and are wholly present at each moment at which they exist. The most common version of four-dimensionalism is perdurantism1, according to which these four-dimensional objects are segmented into temporal parts – shorter lived objects that compose the four-dimensional whole in just the same way that the segments of real earth worms compose the whole worm.
- According to Parsons, a four-dimensionalist need not believe in temporal parts. But ought a four-dimensionalist to believe in temporal parts? This question might be thought uninteresting, insofar as it has largely been answered by force of numbers. But asking it is instructive. For there are reasons to suppose that a non-perdurantist2 four-dimensionalism might provide an attractive middle position between perdu rantism and endurantism3: a position that avoids many of the different counterintuitive costs associated with each of these views. So it is worth determining whether non-perdurantist4 four-dimensionalism is a viable theory of persistence. To that end I develop the most plausible non-perdurantist5 version of four-dimensionalism.
- Ultimately, however, I argue that non-perdurantist6 four-dimensionalism does not offer a plausible middle ground position between perdurantism7 and endurantism8. Further, in considering the reasons why non-perdurantism9 is unappealing, a number of problems are revealed for endurantism10. Much of what is problematic about non-perdurantism11 is equally problematic for endurantism12. What is illuminating is that the analogous problems we discover for endurantism13 are not those that typically constitute objections to the view. This is because evaluating non-perdurantism14 allows us to abstract away from two issues that cloud the debate between three- and four-dimensionalists: first, the idea that three-dimensional objects are wholly present whenever they exist, and the associated problems with cashing out this notion; and second, the idea that three-dimensional objects are strictly identical to themselves at every time at which they exist, and the attendant problems with that notion in the light of change across time. Abstracting away from these issues is fruitful, because frequently with respect to these issues, debate on either side reduces to an appeal to brute intuition leaving the debate stagnant.
- That endurantism15 faces the same problems as non-perdurantist16 four-dimensionalism tells us that the debate between perdurantists17 and endurantists18 has been misplaced. We discover that perdurantism19 is in some sense resilient: as soon as we move away from a perdurantist20 to a non-perdurantist21 four-dimensionalism, the account exhibits fundamental problems. What is wrong with endurantism22 is not that it embraces identity across time, rather, what is problematic is that it is non-perdurantist23. Non-perdurantist24 theories of persistence fail because ultimately, temporal parts are resilient: we need them in any account of persistence.
- I begin by outlining some reasons to find non-perdurantist25 four dimensionalism an attractive view. Then in sections three, four and five I set out a more detailed account of a non-perdurantist26 four-dimensionalism. This allows us, in section six, to see the shortcomings of such a position. In this section I outline a number of key objections to non-perdurantism27, before in section seven arguing that analogous problems arise for endurantism28.
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