Conceptual Structures And Ccc: Linking Theory And Incorporated Argument Adjuncts

In Combinatory Categnrial Grammar (CCG) [Ste90, Ste91], semantic function-argument structures are compositionally produced through the course of a derivation. These s tructures identify, inter alia, which entities play the same roles in different events for expressions involving a wide range of coordinate constructs. This sameness of role (i.e. ~hematie) information is not identified, however, across eases of verbal diathesis. To handle these cases as well, the present paper demonstrates how to adapt the solution developed in Conceptual Semantics [Jac90, Jac91] to fit the CCG paradigm. The essence of the approach is to redefine the Linking Theory component of Conceptual Semantics in terms of CCG categories, so tha t derivations yield conceptual s t ructures representing the desired thematic information; in this way no changes are required on the CCG side. While this redefinition is largely straightforward, an interesting problem arises in the case of Corn ceptual Semantics ' Incorporated Argument Adjuncts. In examining these, the paper shows tha t they cannot be treated as adjuncts in the CCG sense without introducing new machinery, nor without compromising the independence of the two theories. For this reason, the paper instead adopts the more t radi t ional approach of treating them as oblique arguments . 1 I n t r o d u c t i o n Tile present paper represents the first a t t empt to integrate Mark Steedman's theory of Combinatorial Categorial Grammar (CCG) [Ste90, Ste91] with Ray Jackendoff 's theory of Conceptual Semantics [Jac90, ~lac91]. The former is known for its successhd treatment of tong-distance dependencies, coordination, and, more recently, matters of discourse focus relating to intonation---none of which have been treated within Conceptual Semantics. The latter is known for its development of conceptual structures, which are mental representations intended to serve as the link between language and other areas of cognition, e.g. vision, action and inference--which CCG stops short of. Since CCG is a. lexically oriented theory of g rammar , the two are entirely compatible, as well as complementary. The immediate motivation to a t tempt such an integration, and the focus of the present paper, is CCG's incomplete t reatment of sameness of role (i.e. thematic) information. In CCG, semantic function-argument s t ructures are compositionally produced through the course of a derivation. These s t ructures identify, inter alia, which entities play the same roles in different events for expressions involving a wide range of coordinate constructs. For example, the semantic functionargument s t ructure shown in ( lb) is derived for the sentence in ( la) via type-raising, composition, and coordination of the bracketed non-s tandard constituent, following the analysis of Dowty [Dow88]: 1 ( la ) Jack filled [the urn with coffee] and [the thermos with milk]. (lb) (fill' urn' coffee' jack') & (fill' thermos' mill" jack') Of course, such semantic funct ion-argument structures are intended only for illustrative purposes; indeed, according to Steedman, semantic constants like urn ' are "mere placeholders for a real semantics, intended to do no more than illustrate this compositionality." Nevertheless, we may glean from these s tructures the requirement tha t urn ' and thern*os' play the same semantic role, since they are both first arguments to fill', and likewise for coffee' and milk', since they are both second arguments. In the terminology of Conceptual Semantics, these requirements may be restated in terms of thematic roles as follows: urn' and lhermos' share the thematic role Goal in their respective events; like1The semantic role of determiners and tenne will be ignored in this paper. ACT~ DE COLING-92., NANI'ES, 23-28 Aofrr 1992 2 4 6 PROC. OF COLING-92, NANTES, AUG. 23-28, 1992 wise, coffee' and milk' share tile thematic role Theme. 2 Now, while CCG can thus be said to identify thematic information across a wide range of expressions not easily analyzed in other theories, it does not do so across cases of verbal diathesis (i.e, argument structure alternations). For example, consider (2), together with two possible sets of interpretations that follow: (2a) Jack filled the urn {with decaf}. (2b) The urn filled {with decaf}. (2c) Coffee filled the urn {* with decal}. (3a) fill' urn' {decaf~ jack' (35) till' {decaf'} urn' (3c) tilt" urn' coffee' (4a) tiU.' arn' {deck/'} jack' (45) f i l lb'{decaf '} urn,' (4c) fill~' urn' coffee' Here it would not do to derive the function-argument structures shown in (3), as they incorrectly equate semantic roles in some eases, t'br example, the roles of jack" and coffee" are incorrectly said to be the same for Jack filled the urn and Coffee filled the urn. This problem may be avoided by introducing distinct constants ill// ' (with possibly varying arities), as shown in (4). Note, however, that this approach is incomplete, insofar as it fails to equate any semantic roles across the functions til~ ', at least in the absence of further conditions on these functions. To handle these cases as well, the present paper demonstrates how to adapt the solution developed in Conceptual Semantics to fit tile CCG paradigm. This approach may be seen as one method of specifying, in a principled fashion, the further conditions on constants like filli' necessary to give a complete account of thematic role identities. 3 It should not be viewed, however, as a variant of purely syntactic approaches to verbal diathesis, such as the Unaccusative tlypothesis [Bur86] in GB, which posit movement between an underlying and a surface structure and traces to recover thematic roles) 2 This restatetaent is actually a cor~iderable atrengtheldngb as CCG is not committed to anything stronger thmt the individual thematic role view (cf. [Dow91D; thai is, it requi~s no nmre than jack' play the "filler" role, urn' and thermos' play the "filled" role, etc. 3Another viable approach is of course to use ntemffng postulates. A detailed discussion of these alternatives is beyond the scope of tiffs paper (though cf. the discussioa in [dacPO]). 4Agaln, cf. also [J~cgo 3 for independent aa-guments in favor of the Concepttml Sematltics approach. Jack filled the urn ~P: jack ~ (S\NP)/NP:~ilI_a ~ NP/~ Xlurn' . . . . . . . . . . . > NP:urn ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . > S \ N P : f i l l _ a ' urn ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < s : f i l l _ a j urn ~ j a c k ' Figure 1: A simple derivation. The essence of the present approach is to redefine the Linking Theory component of Conceptual Semantics in t e a l s of CCG categories, so that derivations yield conceptual structures representing the desired thematic information; in this way no changes are required on the CCG side. While this redefinition is largely straightforward, an interesting problem arises ill the case of Conceptual Semantics' Incorporated Argument Adjuncts. In examining these, the paper shows that they cannot be treated as adjuncts in the CCG sense without introducing new machinery, nor without compromising the independence of the two theories. For this reason, the paper instead adopts the more traditionM approach of treating them as oblique arguments. 2 P r e l i m i n a r i e s This section reviews the details of CCG mid Conceptual Semmltics needed to understand their integration.