Linguistic and pragmatic constraints on utterance interpretation

To model how people understand language, it becomes necessary to understand not only grammar and logic, but also how people use language to affect their environment. This area of study is known as natural language pragmatics. Speech acts, for instance, are the offers, promises, announcements, and so on that people make by talking. The same expression may be different acts in different contexts, and yet not every expression performs every act. We want to understand how people are able to recognize each other's intentions and implications in saying something. Previous plan-based theories of speech act interpretation do not account for the conventional aspect of speech acts. They can, however, be made sensitive to both linguistic and propositional information. This document presents a method of speech act interpretation which uses patterns of linguistic features (e.g. mood, verb form, sentence adverbials, thematic roles) to identify a range of speech act interpretations for the utterance. These are then filtered and elaborated by inferences about agents' goals and plans. In many cases the plan reasoning consists of short, local inference chains (that are in fact conversational implicatures), and extended reasoning is necessary only for the most difficult cases. The method is able to accommodate a wide range of cases, from those which seem very idiomatic to those which must be analyzed using knowledge about the world and human behavior. It explains how "Can you pass the salt?" can be a request while "Are you able to pass the salt?" is not.