  To the modern eye, Prior’s 1956 possible worlds semantics looks familiar yet also strange. There is no semantic ascent, and there are no frames, models, valuations, satisfaction clauses or truth conditions. Prior’s modal semantics belongs to a pre-modern era, the era of ‘translational’ semantics, a type of semantics that pre-dated the meteoric rise of Tarski-style truth-conditional semantics in the 1960s and 1970s (Copeland 2016). A translational semantics translates the targeted sentences into a more illuminating language, such as Prior’s enriched predicate calculus. For anyone who understands Prior’s augmented predicate calculus, his translational clauses, such as \((\Diamond p)a = \exists x(Uax \amp px),\) offer both an explanation of the meanings of the modal operators and an account of how the meanings of complex sentences (e.g. the S4 and S5 axioms) arise recursively from the meanings of their parts.