Interferring Discourse Relations in Context

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 constraints interact with the other knowledge sources, we draw some general conclusions about the role of domain-specific information, top-down and bottom-up discourse information flow, and the usefulness of formalisation in discourse theory. Introduct ion: T i m e S w i t c h i n g and A m e l i o r a t i o n Two essential parts of discourse interpretation involve (i) determining the rhetorical role each sentence 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 interpretat ion 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 reviewers for their helpful comments. Moreover, the text in (3) in vacuo is incoherent, but becomes coherent in (4)'s context.