Temporal Connectives in a Discourse Context

Temporal Connectives in a Discourse Context Alex Lascarides and .]on Oberlander* Centre for Cognitive Science and Human Communication Research Centre, University of Edinburgh 2, Buccleuch Place, Edinburgh, EH8 9LW Scotland, UK alex, j on@cogsci, ed. ac .uk Abstract We examine the role of temporal connec- tives in multi-sentence discourse. In cer- tain contexts, sentences containing tempo- ral connectives that are equivalent in tem- porai structure can fail to be equivalent in terms of discourse coherence. We account for this by offering a novel, formal mech- anism for accommodating the presupposi- tions in temporal subordinate clauses. This mechanism encompasses both accommoda- tion by discourse aftachme,f and accom- modation by temporal addition. As such, it offers a precise and systematic model of interactions between presupposed material, discourse context, and the reader's back- ground knowledge. We show how the re- sults of accommodation help to determine a discou~e's coherence. 1 Introduction We focus on aspects of the discourse behaviour of the temporal connectives before, after and when. In particular, we note that discourse context can cause sentences which are equivalent in temporal structure to fail to be equivalent in terms of discourse coher- ence. We attempt to explain why context can have this effect. The explanation hinges on the differing presuppositions posted by the differing connectives, and on the novel mechanism whereby background knowledge determines how they are accommodated into the discourse Structure during interpretation. *The support of the Science and Engineering Research Council through project number GR/G22077 is grate- fully acknowledged. HCRC is supported by the Economic and Social Research Council. 2 Temporal Equivalence and Discourse Incoherence First, then, consider the following actual sequence of states and events: in the UK in November 1992, some right-wing Tory backbench MPs were objecting to government policy over the treaty of Maastricht, and threatened to vote against it; the Prime Minister, a Mr John Major, offered them a variety of concessions to win them back, in what the press termed a "charm offensive"; the MPs responded by voting with the government. Call this course of events El. We can combine descriptions of the main eventu- alities in several ways, to reflect the right temporal structure, but only some of these seem pragmatically appropriate: consider in particular these possible de- scriptions of El involving the connectives before, aft fer and tvhe.: (1) The backbenchers were in revolt. (2) a. They were pacified after Major launched a charm offensive. b. ?Major launched a charm offensive be- fore they were pacified. c. They were pacified when Ma- jor launched a charm offensive. d. ?Major launched a charm offensive when they were pacified. There are at least two apparent anomalies, which re- quire explanation. First, one might expect that (2a) and (2b) would be temporally equivalent, both de- scribing El; why, then, does (2b) apparently lead to discourse incoherence? Secondly, it has been argued that A when B permits many possible temporal re- lationships between the eventualities denoted by A and B (cf. Moens and Steedman 1988); it's for …

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