Previous plan‐based models of dialogue understanding have been unable to account for many types of subdialogues present in naturally occurring conversations. One reason for this is that the models have not clearly differentiated between the varoius ways that an utterance can relate to a plan structure representing a topic. In this paper we present a plan‐based theory that allows a wide variety of utterance‐plan relationships. We introduce a set of discourse plans, each one corresponding to a particular way that an (...) utterance can relate to a discourse topic, and distinguish such plans from the set of plans that are actually used to model the topics. By incorporating knowledge about discourse into a plan‐based framework, we can account for a wide variety of subdialogues while maintaining the computational advantages of the plan‐based approach. (shrink)