Multi-speaker utterances and co-ordination in task-oriented dialogue

We investigate task-oriented dialogue where utterances are produced by several agents. Starting out from an example where a directive is initiated by one agent and completed by the addressee, we explain under which conditions co-ordinations of this type can be successful. The explanatory devices developed are 'action schema' and 'sufficiently informative proposition'. We argue that propositions embedded in directives must be sufficiently informative for an agent to execute a task-relevant action. We further suggest that agents' co-ordination on sufficiently informative propositions may be taken as a measure of co-ordination in dialogue. Using this idea, we show how co-ordination in a full task-oriented dialogue develops. Finally, we demonstrate that agents' "pointwise" coordination can be explained using Asher-Morreau defeasible inference, a version of the Lascarides Asher Practical Syllogism (PS), as well as additional principles such as a Co-operativity Principle and a Principle of Transparency, saying 'Make assumed conformity of interests and intentions publicly known'. Our proposals would entail that any theory of dialogue would have to be based on coordination; in addition, the proposals would have repercussions on the notions of proposition, mutuality, and common ground. (c) 2005 Elsevier B.V. All rights reserved.