  During the 1940s, the logic of time was in its infancy. In 1941 Findlay briefly suggested a ‘calculus of tenses’, as explained below, and in 1947 both Łoś, in Poland, and Reichenbach, in the United States, published limited proposals concerning the logic of time (Łoś 1947, Reichenbach 1947; Łoś’s paper was reviewed in English by Hiż 1951; see also Prior 1967a: 12–15, 212–213, and Tkaczyk and Jarmużek 2018). However, neither Łoś nor Reichenbach anticipated the crucial idea of using modal operators to create a formal calculus of time.