MODAL LOGIC BEFORE KRIPKE

100 years ago C.I. Lewis published A Survey of Symbolic Logic, which included an axiom system for a notion of implication which was ‘stricter’ than that found in Whitehead and Russell’s Principia Mathematica. As far as I can tell little notice was taken of this until 1930 when Oskar Becker provided some additional axioms which led Lewis in Symbolic Logic (written with C.H. Langford, 1932) to revise the system he had produced in 1918, and list five systems which could be obtained using Becker’s suggested formulae. The present paper reviews the development of modal logic both before and after 1932, up to 1959 looking at, among other work, Becker’s 1930 article and Robert Feys’s articles in 1937 and 1950. I will then make some comments on the completeness results for S5 found in Bayart and Kripke in 1959; and I will finally look at how modal logic reached New Zealand in the early 1950s in the work of Arthur Prior.