Full Idea
'Existence' can't be glossed as self-identical (critics say) because Pegasus, even while being self-identical, fails to exist.
Gist of Idea
Maybe self-identity isn't existence, if Pegasus can be self-identical but non-existent
Source
José A. Benardete (Metaphysics: the logical approach [1989], Ch.11)
Book Reference
Benardete,José A.: 'Metaphysics: The Logical Approach' [OUP 1989], p.70