Comparatives and Ellipsis

COMPARATIVES AND ELLIPSIS s. G. Puhnan SRI International, and University of Cambridge Computer Laboratory SRI International Cambridge Computer Science Research Centre 23 Miller's Yard, Cambridge CB2 1RQ sgp@cam.sri.com ABSTRACT This paper analyses the syntax and seman- tics of English comparatives, and some types of ellipsis. It improves on other recent analy- ses in the computational linguistics literature in three respects: (i) it uses no tree- or logical-form rewriting devices in building meaning represen- tations (ii) this results in a fully reversible lin- guistic description, equally suited for analysis or generation (iii) the analysis extends to types of elliptical comparative not elsewhere treated. INTRODUCTION Many treatments of the English comparative construction have been advanced recently in the computational linguistics literature (e.g. Rayner and Banks, 1989; Ballard, 1988). This interest reflects the importance of the construction for many natural language applications, especially those concerning access to databases, where it is natural to require information about quantita- tive differences and limits which are most nat- urally expressed in terms of comparatives and superlatives. However, all of these analyses have their de- fects (as no doubt does this one). The most per- vasive of these defects is one of principle: they all place a high reliance on non-compositional methods (tree or formula rewriting) for assem- bling the logical forms Of comparatives even in cases that might be thought to be straightfor- wardly compositional. These devices mean that the grammatical descriptions involved lack, to varying extents, the important property of re- versibility: they can only be used to analyse, not to generate, expressions of comparison. This is a serious restriction on the practic,'d usefulness of such analyses. The analysis presented here of the syntax and compositional semantics of the main instances of the English comparative and superlative is in- tended to provide a fairly theory-neutral 'off the shelf' treatment which can be translated into a range of current grammatical theories. The main theoretical claim is that by factoring out the compositional properties of the construction from the various types of ellipsis also involved, a cleaner treatment can be arrived at which does not need any machinery specific to this construc- tion.. A semantics in terms of generalised quan- tifiers is proposed. SYNTAX Intuitively, a sentence like: John owns more horses than Bill owns seems to consist of two sentences ascribing owns ership of horses, together with a comparison of them, where some material has been omitted. Despite appearances, however, this pre-theoretical intuition is ahnost wholly wrong, both syntacti- cally, and, as we shall see, semantically. The sequence 'more horses than Bill owns' is in fact an NP, and a constituent of the main clause, as can be seen from the fact that it can appear as a syntactic subject, and be conjoined with other simple NPs: [More horses tha~ Bill owns] are sold every day John, Mary, and [more linguists than they could cope with] arrived at the party In order to accommodate example like these we must analyse the whole sequence as an NP, …

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