In 1958 Arnould Bayart, 1911-1998, produced a semantics for first and second-order S5 modal logic, and in 1959 a completeness proof for first-order S5, and what he calls a 'quasi-completeness' proof for second-order S5. The 1959 paper is the first completeness proof for modal predicate logic based on the Henkin construction of maximal consistent sets, and indeed may be the easier application of the Henkin method even to propositional modal logic. The semantics is in terms of possible worlds, which, Bayart (...) notes, can be anything at all. The present paper provides an English translation of both these papers together with an historical introduction and a logical commentary. (shrink)

The paper first proves the completeness of the first-order predicate logic presented in Carnap’s 1946 article ‘Modalities and quantification’. By contrast the modal logic defined by the semantics Carnap produces is unaxiomatisable. One can though adapt Carnap’s semantics so that a standard completeness proof for a Carnapian version of predicate S5 turns out to be available. //.