On vagueness, 4D and diachronic universalism

I offer a new criticism of the argument from vagueness to four-dimensionalism Sider 2001 Sider, Theodore. 2001. Four-Dimensionalism: An Ontology of Persistence and Time, Oxford: Clarendon Press. Crossref] , Google Scholar]. The argument is modelled after an older argument for mereological universalism Lewis 1986 Lewis, David. 1986. On the Plurality of Worlds, Oxford: Blackwell.  Google Scholar] and may be looked upon as a tightened-up and extended version of the latter. While I agree with other critics Koslicki 2003 Koslicki, Kathrin. 2003. The Crooked Path from Vagueness to Four-Dimensionalism. Philosophical Studies, 114: 107–134. Crossref], Web of Science ®] , Google Scholar]; Markosian 2004 Markosian, Ned. 2004. Two Arguments from Sider's Four-Dimensionalism. Philosophy and Phenomenological Research, 68: 665–673. Crossref] , Google Scholar] that the argument from vagueness fails precisely because of this affinity, my recipe for dealing with it is different. I reject the assumption, shared by Sider with his opponents, that synchronic composition and ‘minimal diachronic fusion’ are sufficiently similar to use considerations inspired by the analysis of the former to bear on the latter. My objection to a crucial premise of the argument from vagueness turns on the relevant aspect of dissimilarity between these two cases.