To respond to an utterance, a listener must interpret what others have said and why they have said it. Misunderstandings occur when agents differ in their beliefs about what has been said or why. Our work combines intentional and social accounts of discourse, unifying theories of speech act production, interpretation, and the repair of misunderstandings. A unified theory has been developed by characterizing the generation of utterances as default reasoning and using abduction to characterize interpretation and repair.