Full Idea
An elucidation of transworld identity can be regarded as an elucidation of the boundaries of possibility for ordinary things.
Gist of Idea
Transworld identity concerns the limits of possibility for ordinary things
Source
Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
Book Reference
Forbes,Graeme: 'The Metaphysics of Modality' [OUP 1985], p.97
A Reaction
I presume that if we don't search for some such criterion, we just have to face the possibility that Aristotle could have been a poached egg in some possible world. To know the bounds of possibility, study the powers of actual objects.