From Four‐ to Five‐Dimensionalism

Philosophers have long noticed the similarity of identity over time and identity across worlds. Despite this similarity, analogous views on these matters are not always taken equally seriously. Four‐dimensionalism is one of the most well‐known accounts of identity over time. There is a clear modal analogue of four‐dimensionalism, on which objects are modally extended and their trans‐world identity is a matter of having distinct modal parts located in different possible worlds. Yet this view, which we might call ‘five‐dimensionalism,’ is rarely discussed or defended, in comparison to its temporal counterpart. I argue that five‐dimensionalism is at least as plausible as four‐dimensionalism and deserves serious consideration as an account of trans‐world identity. The strategy is to show that arguments typically used in defence of four‐dimensionalism can be adapted to defend five‐dimensionalism as well. A powerful consideration in favour of four‐dimensionalism is the fact that it provides an elegant and unified solution to a variety of puzzles concerning material coincidence. I show that such puzzles come in equally troubling modal varieties and that five‐dimensionalism provides an equally unified and elegant solution to them. 1