Intentions and Information in Discourse

INTENTIONS AND INFORMATION IN DISCOURSE Nicholas Asher IRIT, Universit4 Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse, CEDEX, France asher@irit, fr Alex Lascarides Department of Linguistics, Stanford University, Stanford, Ca 94305-2150, USA, alex~csli, stanford, edu Abstract This paper is about the flow of inference between com- municative intentions, discourse structure and the do- main during discourse processing. We augment a the- ory of discourse interpretation with a theory of distinct mental attitudes and reasoning about them, in order to provide an account of how the attitudes interact with reasoning about discourse structure. INTRODUCTION The flow of inference between communicative intentions and domain information is often essential to discourse processing. It is well reflected in this discourse from Moore and Pollack (1992): (1)a. George Bush supports big business. b. He's sure to veto House Bill 1711. There are at least three different interpretations. Con- sider Context 1: in this context the interpreter I be- lieves that the author A wants to convince him that (lb) is true. For example, the context is one in which I has already uttered Bush won't veto any more bills. I reasons that A's linguistic behavior was intentional, and therefore that A believes that by saying (la) he will convince I that Bush will veto the bill. Even if I believed nothing about the bill, he now infers it's bad for big business. So we have witnessed an inference from premises that involve the desires and beliefs of A (Moore and Pollack's "intentional structure"), as well as his linguistic behavior, to a conclusion about domain information (Moore and Pollack's "informational struc- ture"). Now consider Context 2: in this context I knows that A wants to convince him of (la). As in Context 1, I may infer that the bill is bad for big business. But now, (lb) is used to support (la). Finally, consider Context 3: in this context I knows that House Bill 1711 is bad for big business, but doesn't know A's communicative desires prior to witnessing his linguistic behaviour. From his beliefs about tile domain, he infers that supporting big business would cause Bush to veto this bill. So, A must. have uttered (la) to support (lb). Hence I realises that A wan~ed him to believe (lb). So in contrast to Contexts 1 and 2, we have a flow of inference from informational structure to intentional structure. This story makes two main points. First, we agree with Moore and Pollack that we must represent both the intentional import and the informational import of a discourse. As they show, this is a problem for current formulations of Rhetorical Structure Theory (RST) (Thompson and Mann, 1987). Second, we go further than Moore and Pollack, and argue that rea- soning about beliefs and desires exploits different rules and axioms from those used to infer rhetorical relations. Thus, we should represent intentional structure and dis- course structure separately. But we postulate rhetorical relations that express the discourse function of the con- stituents in the communicative plan of …

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