Communicative acts and mental state change

Communicative acts in natural language dialogues can be regarded as intentional acts pcrfonncd by a dialogue participant to influence the relevant aspects of the menial stale of a recipient. In this paper a framework is discussed for deriving the beliefs and intentions of a speaker from a certain communicative act. To !his end, the act is expressed in terms of prosodic and textual features of the utterance and connected by means of default rules to the conditions that must be fulfilled by a speaker in order to perform the act felicitously. These conditions are expressed in terms of che beliefs and intentions of the speaker and may be compared with Searle's felicity conditions on speech acts. It is argued lhat some of the Scarlean conditions can be derived from a formalization of general principles of ralional behaviour in information dialogucs.