Operator Arguments Revisited

Certain passages in Kaplan’s ‘Demonstratives’ are often read as constituting an argument for the conclusion that the presence of a non-vacuous sentential operator associated with a certain parameter of sentential truth in a language requires the assertoric contents-cum-compositional semantic values of sentences in that language to vary in truth value with that parameter. Thus, for example, the non-vacuity of a temporal sentential operator ‘always’ would require some of its operands to have assertoric contents that have different truth values at different times. While making no claims about Kaplan’s intentions, we provide several reconstructions of how such an argument might go, focusing on the case of time and temporal operators as an illustration. What we regard as the most plausible reconstruction of the argument establishes a conclusion similar enough to that attributed to Kaplan. However, the argument overgenerates, leading to absurd consequences. We conclude that assertoric contents cannot be compositional semantic values, and argue that once they are distinguished, the argument fails to establish any substantial conclusions. We also briefly discuss a related argument commonly attributed to Lewis, and a recent variant due to Weber.