Inferring Discourse Relations in Context

INFERRING DISCOURSE RELATIONS IN CONTEXT* Alex Lascarides Human Communication Research Centre, University of Edinburgh, 2 Buccleuch Place, Edinburgh alex@cogsc£, ed. ac. uk Nicholas Asher Center for Cognitive Science, University of Texas, Austin, Texas 78712 asher@cgs, utexas, edu :Ion Oberlander Human Communication Research Centre, University of Edinburgh, 2 Buccleuch Place, Edinburgh jonecogec£, ed. ac .uk Abstract We investigate various contextual effects on text interpretation, and account for them by providing contextual constraints in a logical theory of text interpretation. On the basis of the way these con- straints interact with the other knowledge sources, we draw some general conclusions about the role of domain-specific information, top-down and bot- tom-up discourse information flow, and the use- fulness of formalisation in discourse theory. Introduction: Time Switching and Amelioration Two essential parts of discourse interpretation in- volve (i) determining the rhetorical role each sen- tence plays in the text; and (ii) determining the temporal relations between the events described. Preceding discourse context has significant effects on both of these aspects of interpretation. For example, text (1) in vacuo may be a non-iconic explanation; the pushing caused the falling and so explains why Max fell. But the same pair of sentences may receive an iconic, narrative in- terpretation in the discourse context provided by (2): John takes advantage of Max's vulnerability while he is lying the ground, to push him over the edge of the cliff. (1) Max fell. John pushed him. (2) John and Max came to the cliff's edge. John applied a sharp blow to the back of Max's neck. Max fell. John pushed him. Max rolled over the edge of the cliff. a The support of the Science and Engineering Research Council through project number GR/G22077 is gratefully acknowledged. HCRC is supported by the Economic and SociM Research Council. We thank two anonymous re- viewers for their helpful comments. Moreover, the text in (3) in vacuo is incoherent, but becomes coherent in (4)'s context. (3) (4) ?Max won the race in record time. He was home with the cup. Max got up early yesterday. He had a lit- tle bite to eat. He had a light workout. He started the tournament in good form. He won the race in record time. He was home with the cup. He celebrated until late into the evening. So we can see that discourse context can time switch our interpretation of sentence pairs, (cf. (1) and (2)); and it can ameliorate it, (cf. (4)'s improvement of (3)). The purpose of this paper is two-fold: we attempt to capture formally these aspects of discourse context's impact on clausal attachment; and in the process, we assess whether the structure of the domain being described might be sufficient alone to account for the phenomena. Of course, the idea that discourse context con- strains the discourse role assigned to the current clause is by no means new. Reference resolution is influenced by discourse structure (cf. Grosz and Sidner 1986:188 for a very clear case); and it in turn influences discourse …

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