This paper describes some of the basic cooperative mechanisms of dialogue. Ideal cooperation is seen as consisting of four features (cognitive consideration, joint purpose, ethical consideration and trust), which can also to some extent be seen as requirements building on each other. Weaker concepts such as &&coordination'' and &&collaboration'' have only some of these features or have them to lesser degrees. We point out the central role of ethics and trust in cooperation, and contrast the result with popular AI accounts of collaboration. Dialogue is also seen as associated with social activities, in which certain obligations and rights are connected with particular roles. Dialogue is seen to progress through the written, vocal or gestural contributions made by participants. Each of the contributions has associated with it both expressive and evocative functions, as well as speci"c obligations for participants. These functions are dependent on the surface form of a contribution, the activity and the local context, for their interpretation. We illustrate the perspective by analysing dialogue extracts from three di!erent activity types (a travel dialogue, a quarrel and a dialogue with a computer system). Finally, we consider what kind of information is shared in dialogue, and the ways in which dialogue participants manifest this sharing to each other through linguistic and other communicative behaviour. The paper concludes with a comparison to other accounts of dialogue and prospects for integration of these ideas within dialogue systems.
2000 Academic Press