Lewis on Duplication and External Relations

Title: Lewis on Duplication and External Relations

By Cody Gilmore (UC Davis, Philosophy)

Date: Thursday, May 7, 2026

Time: 1530-1700

Room: Humanities Seminar Room (H-232)

Abstract: David Lewis influentially defines intrinsicality in terms of duplication and duplication in terms of perfect naturalness:

(D1) An intrinsic property is one that can never differ between two duplicates. (1986: 62)
(D2) Two things are duplicates iff (1) they have exactly the same perfectly natural properties and (2) their parts can be put into correspondence in such a way that corresponding parts have exactly the same perfectly natural properties and stand in the same perfectly natural relations. (1986: 61)

I claim that there are possible worlds at which time is circular and its topology is characterized by a perfectly natural three-place or four-place temporal ordering relation. I then argue that this generates surprising counterexamples to the joint sufficiency of conditions (1) and (2) for duplication. I explore some potential repairs and trace their implications, with special attention to the notion of an external relation. (This talk is based on joint work with Tania Aiyar.)

About the speaker: Cody Gilmore is Professor of Philosophy at the University of California, Davis. He works in topics in metaphysics, especially: properties, relations, and propositions; essence and grounding; time and identity; and formal theories of parthood and location. His work has appeared in such journals as the Australasian Journal of Philosophy, Mind, Philosophical Studies, and Oxford Studies in Metaphysics.

Organized by the Department of Philosophy