Full Idea
The thesis of Relativity of Identity (which I steadfastly oppose) ..suggests that it makes all the difference to keeping track of continuants through space and time which concept one subsumes something under.
Gist of Idea
Relativity of Identity makes identity entirely depend on a category
Source
David Wiggins (Sameness and Substance Renewed [2001], 1.1)
Book Reference
Wiggins,David: 'Sameness and Substance Renewed' [CUP 2001], p.22
A Reaction
[Geach I take to be the villain of this idea] The point is that identity is entirely relative to the sortal concept, where Wiggins wants to make identity a combination of the object itself and our concept of it (I think).