Full Idea
The characteristic of B has the form φ⊃□◊φ. ...Even if these axioms are necessarily true, it seems logically possible for p to be true while the proposition that p is necessarily possible is at the same time false.
Gist of Idea
In B it seems logically possible to have both p true and p is necessarily possibly false
Source
Nathan Salmon (The Logic of What Might Have Been [1989], Intro)
Book Reference
Salmon,Nathan: 'Metaphysics, Mathematics and Meaning' [OUP 2005], p.130
Related Idea
Idea 14667 System B has not been justified as fallacy-free for reasoning on what might have been [Salmon,N]