Full Idea
Modal logic is not an extensional language.
Gist of Idea
Modal logic is not an extensional language
Source
Charles Parsons (A Plea for Substitutional Quantification [1971], p.159 n8)
Book Reference
'Philosophy of Logic: an anthology', ed/tr. Jacquette,Dale [Blackwell 2002], p.159
A Reaction
[I record this for investigation. Possible worlds seem to contain objects]