 In logic and in many of the investigations of logical empiricists in the first two-thirds of the twentieth century, artificial languages were the focus of attention. First the predicate calculus, and then various extensions of it incorporating modal and temporal operators seemed the appropriate linguistic vehicles for clear-thinking philosophers. Issues about the use of natural languages were often thought to be beyond the scope of the proof-theoretic and model-theoretic tools developed by logicians. As Stalnaker put it in 1970, 