Full Idea
In the range of modal systems for which Saul Kripke has provided a semantics, no essentialist sentence is a theorem. Furthermore, there are models for which such sentences are demonstrably false.
Gist of Idea
Essentialist sentences are not theorems of modal logic, and can even be false
Source
Ruth Barcan Marcus (Essential Attribution [1971], p.188)
Book Reference
-: 'Nous' [-], p.188