Local Information in Discourse

Abstract

This dissertation argues that the interpretation of modals, expressions like “might,” “should,” and “must,” are constrained by their local context. For epistemic modals, local contexts bound the admissible domains of modal quantification. In Chapter 2, we use this fact to explain why epistemic “must” is weaker than the □ operator from epistemic modal logic. For root (i.e., non-deontic) modals, local contexts restrict the domain of quantification. In Chapter 3, we show this yields a solution to the Samaritan Paradox concerning why deontic modals do not inherit presuppositions under entailment. In Chapter 4, we propose a solution to the “if ?, ought ?” problem based on default logic. According to this solution, “ought”’s ordering source consists of default rules and the domain consists of the conclusion of the defaults triggered in the local context.