  A propositional language is built up from propositional letters, \(P, Q,\ldots\), using  \(\wedge ,   \vee , \supset , \neg\) and other propositional connectives, and \(\Box\) (necessary) and \(\Diamond\) (possible) as modal operators. These operators can be thought of as alethic, deontic, temporal, epistemic—it will matter which eventually, but it does not at the moment. Likewise there could be more than one version of \(\Box\), as in a logic of knowledge with multiple knowers—this too doesn’t make for any essential differences.