Susanne Bobzien

In my talk I offer a mildly revisionist logic of identity that makes room for the possibility of vague objects at the level of logic without undermining the use of the identity relation in mathematics. The paper challenges Evans’s infamous and still widely accepted 1978 argument that indeterminate identity is incoherent and that any coherent notion of identity must be governed by the modal system S5, with a determinateness operator in lieu of the necessity operator. Building on a suggestion by Ken Akiba (2014) and my own view on vagueness (Bobzien 2025), the talk replaces Evans’s S5 with something a little more flexible.

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