 Possible world semantics is built upon  Tarski’s  (1936, 1944) epochal theory of truth in the first half of the twentieth century. Tarski’s theory provided a rigorous account of the fundamental semantic connections between the languages of classical logic and non-linguistic reality that determine the truth conditions for the sentences of those languages. By generalizing Tarski’s theory to modal  languages,[29]  possible world semantics promised an equally rigorous account of the semantic connections between those languages and modal reality, and thereby an equally rigorous account of modal truth conditions. It is illuminating therefore to start with an account of Tarskian semantics.