Full Idea
For each instance of identity or failure of identity, there must be facts in virtue of which that instance obtains. ..Enough has been said to lend this doctrine some plausibility.
Gist of Idea
In all instances of identity, there must be some facts to ensure the identity
Source
Graeme Forbes (The Metaphysics of Modality [1985], 5.5)
Book Reference
Forbes,Graeme: 'The Metaphysics of Modality' [OUP 1985], p.130
A Reaction
Penelope Mackie picks this out from Forbes as a key principle. It sounds to be in danger of circularity, unless the 'facts' can be cited without referring to, or implicitly making use of, identities - which seems unlikely.