Persistence in Time No person ever steps into the same river twice—or so goes the Heraclitean maxim. Obscure as it is, the maxim is often taken to express two ideas. The first is that everything always changes, and nothing remains perfectly similar to how it was just one instant before. The second is that nothing … Continue reading Persistence in Time →.

Some philosophers say that in special relativity, four-dimensional stuff is invariant in some sense that three-dimensional stuff is not. I show that this claim is false.

Relativity theory is often said to support something called ‘the four-dimensional view of reality’. But there are at least three different views that sometimes go by this name. One is ‘spacetime unitism’, according to which there is a spacetime manifold, and if there are such things as points of space or instants of time, these are just spacetime regions of different sorts: thus space and time are not separate manifolds. A second is the B-theory of time, according to which the (...) past, present, and future are all equally real and there is nothing metaphysically special about the present. A third is perdurantism, according to which persisting material objects are made up of different temporal parts located at different times. We sketch routes from relativity to unitism and to the B-theory. We then discuss some routes to perdurantism, via the B-theory and via unitism. (shrink)

Material objects extend through space by having different spatial parts in different places. But how do they persist through time? According to some philosophers, things have temporal parts as well as spatial parts: accepting this is supposed to help us solve a whole bunch of metaphysical problems, and keep our philosophy in line with modern physics. Other philosophers disagree, arguing that neither metaphysics nor physics give us good reason to believe in temporal parts.

This thesis is composed of three essays on the perdurantist approach to persistence and identity over time. In Chapter 1, I discuss how the following papers are to be understood as parts of a unified perdurantist account of persistence over time. This chapter also outlines some of my philosophical assumptions and provides some background information about the metaphysics of persistence. In Chapter 2, I respond to the objection that the worm theory is unable to account for our intuitions about ordinary (...) counting sentences. I do this by invoking the standard linguistic phenomenon of covert quantifier domain restriction and supplementing the worm theory with situation semantics. My version of the worm theory makes our intuitive judgements come out true, and it does so well enough that there is no need to adopt the stage theory or revisionary theories of counting. Furthermore, my version of the worm theory offers a unified account of event- and object-related counting. Chapter 3 focuses on a commonly neglected difference between different kinds of perdurantism, which are differences in mereological priority. I discuss three different views: parts-first perdurantism, no-priority perdurantism, and wholes-first perdurantism. I briefly outline all three views and some of the motivations for each of them. I fend off objections from and motivations for no-priority perdurantism. I also contend that intraperdurantist debates about phenomenology ought not to be framed with respect to these forms of perdurantism. Instead, I suggest that the relativity of simultaneity presents an interesting scenario for parts-first and wholes-first perdurantists. I respond to Thomas Pashby’s arguments against the doctrine of temporal parts in Chapter 3. Pashby argues that metaphysicians ought to give an account of how quantum systems persist over time and that nonrelativistic quantum mechanics is incompatible with perdurantism. I contend that his arguments rely on controversial, non-standard assumptions about the existence and importance of time observables. I demonstrate that perdurantists have no problem giving an account of how quantum systems persist over time in reference to an external time parameter. Finally, I conclude with a summary of my arguments and some thoughts about directions for future research. (shrink)