Full Idea
Counterpart-theoretic modal semantics allows for the retention of S5 modal propositional logic, at a considerable cost.
Gist of Idea
The unsatisfactory counterpart-theory allows the retention of S5
Source
Nathan Salmon (The Logic of What Might Have Been [1989], V n18)
Book Reference
Salmon,Nathan: 'Metaphysics, Mathematics and Meaning' [OUP 2005], p.149
A Reaction
See the other ideas in this paper by Salmon for his general attack on S5 as the appropriate system for metaphysical necessity. He favours the very modest System T.