 Kaplan (1995) makes use of a related observation to raise a problem for the standard model theory for quantified propositional modal logic. He observed, in particular, that if \(Q\) is a sentential operator of the appropriate sort, then the sentence (K) below is not satisfiable in anny possible worlds model \(\langle W, \mathcal{I} \rangle\) consisting of a set of possible worlds \(W\) and an interpretation function, \(\mathcal{I}\) assigning a set of sets of possible worlds to the sentential operator: