 An immediate consequence of MSA is to render many instances of \(\Box\Diamond\) contingent. For, at an Adams-free world \(w,\) \(\neg \sfE!\sfa,\) for example, is true so, by MSA both \(\neg\Diamond\neg \sfE!\sfa\) and \(\neg\Box\neg \sfE!\sfa\) are true at \(w\). So, given MSA, it appears that the equivalence between necessary truth and impossible falsehood holds at a world only for the propositions that exist there, i.e., in Prior’s terminology, the propositions that are  statable  there. Because, for the strict actualist, necessarily, a proposition exists if and only if all of its subjects exist, no new sentential operator is needed to express propositional existence; a simple counterpart to SDef* will do: