  There was a two-way traffic of ideas. A constant domain was assumed in Kripke’s 1959 ‘A Completeness Theorem in Modal Logic’, and Kripke suspects that Time and Modality first interested him in the problem of treating variable domains. He worked on Prior’s suggestion—formalised in Prior’s system \(Q\)—that variable domains might lead to truth-value gaps even at the level of propositional logic, although Kripke did not pursue this approach in his published material. Further, Kripke thinks it probable that Prior’s work on many-valued matrices in Time and Modality gave him the idea of converting possible worlds models into many-valued matrices, an approach he followed in his 1963 paper ‘Semantical Analysis of Modal Logic I: Normal Modal Propositional Calculi’.