Full Idea
We may say it makes no sense to say that Socrates exists at a world, if there is in principle no way of identifying him. ...But this is confused. To suppose Agnew was a precocious baby, we needn't be able to pick him from a gallery of babies.
Gist of Idea
It doesn't matter that we can't identify the possible Socrates; we can't identify adults from baby photos
Source
Alvin Plantinga (Transworld Identity or worldbound Individuals? [1973], I)
Book Reference
'The Possible and the Actual', ed/tr. Loux,Michael J. [Cornell 1979], p.152
A Reaction
This seems a good point, and yet we have a space-time line joining adult Agnew with baby Agnew, and no such causal link is available between persons in different possible worlds. What would be the criterion in each case?