Mutual Beliefs in Conversational Systems: Their Role in Referring Expressions

Shared knowledge and beliefs affect conversational situations in various ways. One aspect in which they play a role is the choice of referring expressions. It is of interest to analyse this role since a natural language system must be able to decide when it can use a particular referring expression; or alternatively what a particular expression refers to. In this paper we attempt to formally characterise conditions for these. Specifically, we differ with the traditional notion of mutual knowledge and belief, state a conversational conjecture that convinces us to do so, express a weakened notion in a formal system for reasoning about knowledge, and show how this might be used to decide on satisfactory referring expressions. It is desirable to express a weakened notion of mutual belief that parallels that for mutual knowledge; this aspect is currently being investigated.