Temporal Coherence and Defeasible Knowledge

We discuss data involving the temporal structure of connected discourse. Questions are raised about the relation between clause order in discourse and causal order in the world, and about the coherence of certain discourses. We maintain that interpretation is contextually influenced by knowledge of the world and of pragmatics, and that the role of this knowledge should be formalised via a defeasible logic. It transpires that a constrained set of reasoning patterns underlies the retrieval of certain temporal structures. Not all defeasible logics capture the set; the data help choose between candidate logics. We demonstrate that an adequate logic characterises when a text is temporally coherent, reliable and unambiguous relative to the context. We also discuss defeasible reasoning in language generation, and some consequences for the semantics-pragmatics interface.