Full Idea
Forbes argues that, unless we posit individual essences, we cannot guarantee that identities across possible worlds will be appropriately grounded in other properties.
Gist of Idea
Only individual essences will ground identities across worlds in other properties
Source
report of Graeme Forbes (The Metaphysics of Modality [1985]) by Penelope Mackie - How Things Might Have Been 2.4
Book Reference
Mackie,Penelope: 'How Things Might Have Been' [OUP 2006], p.25
A Reaction
There is a confrontation between Wiggins, who says identity is primitive, and Forbes, who says identity must be grounded in other properties. I think I side with Forbes.