On Discourse Relations, Rhetorical Relations And Rhetoric

Discourses are the collaborative activities of (human) agents who have purposes for communicating. Discourse structure includes the purposes of those agents, which I take, following [GroszSid86], to be formally expressible as intentions and beliefs. While the theory of discourse structures has influenced how many computational linguists think about discourse processing, it does not preclude careful consideration of rhetorical function in discourses. Nor does it settle the question of how intentions are conveyed by particular utterances in particular genres of discourse. In recent research I have been studying discourses that occur when people communicate about their collaboative activities. These people are collaborating not only to make the discourse happen, but to get something done together in the world. Following on the model of SharedPlans in [GroszSid90, GroszKra93], I have asked, how is it that agents use language to come to hold the beliefs and intentions specified by the SharedPlan model as necessary for successful collaboration? Using naturally occurring conversations of human agents collaborating, I have observed that their discourses cycle through a series of proposals, rejections, assents, counters, modifications and retractions. To clarify this observation, I have devised an artificial language of negotiation [Sidner92] whose sentences are messages containing proposals of propositions, rejections of propositions, etc. The semantics of these messages is specified in terms of beliefs, especially mutual belief, and intentions that the discourse participants come to hold about the propositional content of the message. Along with the language is an "environment" for interpretation that keeps track of accepted, open and rejected proposals. Using this language I have created artificial conversations in which the beliefs and intentions of the participants are fully evident. Such conversations have some of the richness of naturally occurring ones, though they lack such attentional devices of human discourse as c u e phrases. They also contain more redundancy than human discourse; in the artificial language individual utterances can not serve several functions at once, as is very common in natural human discourse. I maintain as a working hypothesis that the negotiation language can model naturally occuring discourses as cycles of negotiations. Under this hypothesis, the recognition that an utterance serves as a proposal as opposed to a counterproposal, for example, is determined not by the relation of the utterance to previous utterances. It is determined by recognition of beliefs and intentions conveyed by the utterance and by the current discourse state with respect to beliefs and intentions (e.g. which beliefs are not yet mutually believed, which are, and which cannot be because one discourse participants holds that the belief is false); these together indicate how the beliefs and intentions of the current utterance operate as proposals, counterproposals, rejections and the like. As a model of human discourse, the negotiation language provides a fine-grained model of the beliefs and intentions and relations among them that is conveyed in individual utterances. It does not eliminate the need for recognizing what role the particular beliefs and intentions conveyed play in the agents' plans, especially in their SharedPlans, and hence plan recognition is still critical. Recent work by Lochbaum [Lochbaum93] provides an outlook on plan recognition for collaborative activity. The negotiation language might appear to be similar to relations in RST and other theories because terms such as proposing, counterproposing and rejection seem similar to, for example, Mann