Can, Should, Will

Abstract

Abstract This is the first chapter in Part II—on complex logics—and it raises one of the book’s key issues. We study problems for Hume’s Law stemming from the interaction between deontic and modal operators (e.g. ought implies can) by looking at parallel interactions between tense and modal operators, and in particular will implies can. This chapter sharpens these issues by developing a hybrid tense-modal logic which validates these claims. It identifies four possible responses to the counterexample: argue that the premises are really Future, that the conclusion is not Future, deny the validity of the argument and modify the theorem to admit of exceptions.