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<?xml version="1.0" standalone="yes"?> <Paper uid="C90-3018"> <Title>GENERATING CONNECTIVES</Title> <Section position="4" start_page="0" end_page="0" type="relat"> <SectionTitle> 2. PREVIOUS WORK ON CONNECTIVE DESCRIPTION </SectionTitle> <Paragraph position="0"> The most basic constraint on connection is often referred to as homogeneousness condition: two propositions can be conjoined if &quot;they have something in common.&quot; Which features of the conjuncts must be homogeneous is a difficult question: (Chomsky, 1957, p.36) stated a constraint on syntactic homogeneousness (conjuncts must be &quot;of the same type&quot;); a purely syntactic constraint is, however, largely insufficient to satisfy the needs of a text generation system, since file decision to conjoin must be made before the syntactic structure of the conjuucts is determined. (Lakoff, 1971) proposed a semantic approach to the problem of homogeneousness: conjuncts must have a &quot;common topic&quot; for conjunction to be possible (p. 118). Based on this definition of homogeneousness, she distinguished between a &quot;semantic&quot; meaning of&quot;but&quot; (to express a semantic opposition) and a pragmatic usage of &quot;but&quot; (to deny expectations), for eases which would not satisfy the homogeneousness constraint (e.g., &quot;John is rich but dumb&quot;). Such a distinction between a semantic and a pragmatic analysis of connectors is criticized in (Abraham, 1979, p.104) (Lang, 1984, pp172ff) and (Ducrot et al, 1980). Lang (1984) presents a general semantics for conjunction that does not distinguish between pragmatic (or contextual) and semantic levels.</Paragraph> <Paragraph position="1"> Lang attributes to conjunctions an operative semantics: conjunctions' meanings are sets of &quot;instructions&quot; fbr &quot;carrying out certain mental operations&quot; (p. 96) 2. The ~A similar operative approach is advocated in Ducrot, 1983)</Paragraph> <Paragraph position="3"> meaning of connectors is a &quot;program&quot; that controls how a &quot;common integrator&quot; can be constructed from the meaning of each conjunct. In our work, we use a similar approach for the definition of connectives, but, since we work on generation (as opposed to interpretation), we describe the meaning of connectives as sets of constraints that must be satisfied between the conjuncts as opposed to &quot;instructions.&quot; We use the notion of thematization procedure to account for the homogeneousness condition (of. Section 5). In this paper, we concentrate on the distinctions between similar connectives rather than on the general properties of the class of connectives.</Paragraph> <Paragraph position="4"> Work on the structure of discourse (Cohen, 1984, Reichman, 1985, Grosz & Sidner, 1986) has identified the role of connectives in marking structural shifts. This work generally relies on the notion that hearers maintain a discourse model (which is often represented using stacks). Connectives give instructions to the hearer on how to update the discourse model. For example, &quot;now&quot; (Hirschberg & Litman, 1987) can indicate that the hearer needs to push or pop the current stack of the model. When used in this manner, connectives are called &quot;cue (or clue) words.&quot; This work indicates that the role of connectives is not only to indicate a logical or conceptual relation, but also to indicate the structural organization of discourse. The distinction between cue and non-cue usages is an important one, and we also attempt to capture cue usages, but the structural indication (which often has the form of just push or pop) under-constrains the choice of a cue word -. it does not control how to choose among the many markers indicating a pop.</Paragraph> <Paragraph position="5"> Halliday (Halliday, 1985) proposes that the connection between clauses can be described on three dimensions: taxis, expansion and projection. This model is implemented in the Nigel system (Mann & Matthiessen, 1983). It provides a fine-grained classification of a broad set of connectives. However, labels used to describe the type of relation between two propositions within the expansion system are similar to rhetorical relations and precise definitions of these relations, to date, have tended to be subjective.</Paragraph> <Paragraph position="6"> Like Halliday, we also attempt to provide a fine-grained characterization of connectives and our model has features that are similar to Halliday's tccds and projection systems. However, the use of argumentative features and a thematization procedure allows us to avoid reliance on rhetorical relations.</Paragraph> <Paragraph position="7"> Our work is influenced by work in pragmatics on implicature (Levinson, 1983, Karttunen & Peters, 1979) which proposed a two-level representation of utterances (propositional content and implicatures). It is also based on a &quot;multi-dimensional&quot; description of utterances and describes connectives as devices acting on each pragmatic dimension.</Paragraph> <Paragraph position="8"> &quot;But&quot; and &quot;although&quot; can be distinguished by their influence on the discom~e structure in which they are embedded. We draw upon a theory of conversation organization common in conversation analysis (Sinclair & Coulthard, 1975, Taylor and Cameron, 1987~ Roulet et al, 1985, Moeschler, 1986) to explain this distinction. The model describes conversation as a hierarchical structure and defines three levels of constituents: speech acts, move and exchange. A move correspond s to a turn of a speaker in a conversational exchange between two or more speakers. It is made up of several speech acts.</Paragraph> <Paragraph position="9"> In the structure of a move, one speech act is dh'ective; all others are subordinate - they modify or elaborate the directive act (Roulet et al, 1985). Intuitively, the directive act is the reason why the speaker started speaking. It constrains what can follow the move in the discourse. While a move may consist of several sub~ ordinate speech acts in addition to the directive act, the directive controls the possibilities for successive utterances. Thus, it detemfines what is accessible in the structure of the preceding discourse.</Paragraph> <Paragraph position="10"> To see how this characterization of discourse can explain the distinction between &quot;but&quot; and &quot;although,&quot; consider the following examples:</Paragraph> <Paragraph position="12"> although he is smart. Let's hire him.</Paragraph> <Paragraph position="13"> (2) He failed the exam, but he is smart. Let's hire him.</Paragraph> <Paragraph position="14"> In both (1) and (2), the first sentence expresses a contrastive relation between two propositions. But, the fill sequence (2) is coherent, whereas the sequence (1) sounds peculiar in most situations. This can be ex~ plained by the fact that in &quot;P but Q&quot; Q has directive status while in &quot;P although Q,&quot; Q has subordinate status. In (2) then, &quot;he is smart&quot; has directive status, whereas in (1) it is subordinate. Therefore, the argumentative o6entation of the complex sentence as a whole in (l) is the argumentative orientation of &quot;he failed the exam&quot; and it is the argumentative orientation of &quot;he is smart&quot; in (2). The conclusion (let's hire him) is only compatible with &quot;he is sinai,.&quot; This distinction is similar to Halliday's taxis system (the classic subordinate/coordinate distinction) but operates at a different level. Although &quot;but&quot; is a conjunction, meaning that P and Q have the same syntactic status, P and Q have a different influence on the following discourse. We therefore require the input to the surface generator to indicate the &quot;point&quot; of a move, but to leave the syntactic status of each proposition unspecified. This more delicate decision is made by the surface generator.</Paragraph> </Section> class="xml-element"></Paper>