Full Idea
Even the conventionally accepted system B, which is weaker than S5 and independent of S4, has not been adequately justified as a fallacy-free system of reasoning about what might have been.
Gist of Idea
System B has not been justified as fallacy-free for reasoning on what might have been
Source
Nathan Salmon (The Logic of What Might Have Been [1989], Intro)
Book Reference
Salmon,Nathan: 'Metaphysics, Mathematics and Meaning' [OUP 2005], p.129
Related Idea
Idea 14668 In B it seems logically possible to have both p true and p is necessarily possibly false [Salmon,N]