Proposition p is meaningful relative to the collection of possible worlds W if and only if there exist w, w’ in W such that p is true in the possible world w and false in the possible world w’.
Then the question become: to be able to reason in all generality what collection of possible worlds should one use?
Proposition p is meaningful relative to the collection of possible worlds W if and only if there exist w, w’ in W such that p is true in the possible world w and false in the possible world w’.
Then the question become: to be able to reason in all generality what collection of possible worlds should one use?
That’s a very hard question.