Persistence and presentism

The ‘friends of temporal parts’ and their opponents disagree about how things persist through time. The former, who hold what is sometimes called a ‘4D’ theory of persistence, typically claim that all objects that last for any period of time are spread out through time in the same way that spatially extended objects are spread out through space — a different part for each region that the object fills. David Lewis calls this manner of persisting ‘perdurance’. The opposing, ‘3D’ theory has it that at least some objects do not persist in this manner; they ‘endure’ through time by ‘being wholly present at more than one time’.1 A related dispute pits ‘presentists’ against ‘non-presentists’. Presentists hold that the only things that really exist are those that exist now, at the present moment; and nonpresentists believe in something like a ‘block-universe’ in which non-simultaneous objects and events nevertheless co-exist (in a tenseless or non-temporal sense). Of late, the relations between these four positions have come under considerable scrutiny.2 As Ned Markosian has pointed out, it would be surprising if commitment to a perdurance or endurance theory of persistence automatically foreclosed one’s options in the presentism—non-presentism debate. But, says Markosian, that is just what the standard formulations of the perdurance and endurance theories imply.3 David Lewis has set the terms of the debate; in his usage, someone who thinks that all persisting objects endure would be said to hold the following.