Advanced Topics in HPSG∗ Andreas Kathol Adam Przepiórkowski Jesse Tseng 1 Introduction This chapter presents a survey of some of the major topics that have received attention from an HPSG perspective since the publication of Pollard and Sag (1994). In terms of empirical cover- age (of English and other languages) and analytical and formal depth, the analyses summarized here go well beyond the original theory as defined in Pollard and Sag (1987) and (1994), although these naturally remain an indispensable point of reference.1 We will have to make a biased choice among the possible topics to cover here, and the pre- sentation will of course be colored by our own point of view, but we hope that this chapter will give the reader a reasonable idea of current research efforts in HPSG, and directions for further exploration of the literature. In keeping with HPSG’s emphasis on rich lexical descriptions, the first section (§2) concen- trates on the licensing of dependents by lexical heads. We begin with a discussion of the con- ceptual separation between argument structure and valence in current HPSG work. We examine how the the traditional distinction between arguments and adjuncts fits into this model, and then we turn to the highly influential idea of argument composition as a mechanism for dynamically determining argument structure. In §3, we concentrate on issues of linear order, beginning with lexicalist equivalents of con- figurational analyses and then considering more radical departures from the notion of phrase structure. The topics covered in §4 all have to do with ‘syntactic abstractness’. On the one hand, most work in HPSG avoids the use of empty categories in syntactic structure, preferring concrete, surface-based analyses. On the other hand, there is a current trend towards construction-based approaches, in which analyses are no longer driven only by detailed lexical information, but rely crucially on the definition of phrasal types, or constructions. One of the distinctive design features of HPSG is its integrated view of grammar. Informa- tion about syntax, semantics, morphology/phonology, and (potentially) all other components of the grammar represented in a single structure, with the possibility of complex interactions. In §5 we discuss a number of recent developments in the analysis of the syntax-semantics-pragmatics interface, in particular the treament of scope and illocutionary force, as well as information struc- ture and the representation of speakers’ beliefs and intentions. The discussion of grammatical ∗We would like to thank Bob Borsley, Miriam Butt, Ivan Sag, and especially Georgia Green for extensive com- ments on an earlier draft of this article. All remaining errors are ours. 1 interfaces continues in in §6, devoted to interactions between syntax and morphology. We con- clude the chapter with a summary of recent developments in the formal logical foundations of HPSG (§7). 2 Argument Structure One of the most significant conceptual changes distinguishing HPSG from Generalized Phrase Structure Grammar is the treatment of combinatorial properties. In GPSG, lexical items carry a numerical index that identifies the subcategorization frame in which they can occur, and there is a distinct immediate dominance rule for each subcategorization type, resulting in a large number of such rules for head-complement structures. In contrast, lexical descriptions in HPSG include a detailed characterization of their combinatorial potential encoded in a valence feature, and thus a much smaller set of highly general immediate dominance schemata is sufficient. In this way, HPSG has an affinity with Categorial Grammar, where the categories themselves are complex and encode combinatorial properties, allowing the assumption of a small number of general combination mechanisms. A number of linguistic problems have since been explored in HPSG and solutions have been developed that have significantly refined the original ideas and provided new insights into the nature of valence. 2.1 Valence and Argument Structure One significant development since the original presentation of the theory is the separation of the notions of valence and argument structure. In HPSG1 and HPSG2, valence was encoded in a single attribute, SUBCAT, containing a list of all syntactically selected dependents. Borsley (1987) pointed out, however, that this approach did not allow syntactic functions to be reliably distinguished. For example, the subject was originally defined as “the single remaining element on SUBCAT”, but this incorrectly identifies some prepositional complements and nominal specifiers as subjects. Borsley’s proposals for treating syntactic functions as primitive notions, and splitting the SUBCAT list into three valence lists, SUBJ(ECT), SPECIFIER (SPR), and COMP(LEMENT)S, were adopted in HPSG3, and since then most authors assume these three lists as part of a complex VALENCE attribute.2 The technical consequence of this move is that the head-complement, head-subject, and head- specifier schemata refer to the appropriate valence lists, rather than particular configurations of SUBCAT, and the SUBCAT Principle is replaced by the correspondingly more complex Valence Principle. An alternative default formulation of this principle is proposed by Sag (1997),3 later incorporated into the default Generalized Head Feature Principle (Ginzburg and Sag, 2000). This approach offers a more economical notational representation (at the price of additional formal machinery for allowing default unification), but it can be argued that the essential content of the original Valence Principle—that synsem objects are removed from the valence lists when they are syntactically realized—is then encoded in a piecemeal fashion in the definitions of the individual ID schemata. 2 The decision to split syntactic valence into three lists makes it possible to express mismatches between the syntactic function of a constituent and the way that it is realized in the syntactic struc- ture. This possibility has been exploited mainly in analyses where the synsem of the grammatical subject is encoded in the COMPS list. As a result, the subject is realized not by the head-subject schema, but by the head-complement schema. This has been proposed for verb-initial languages like Welsh (Borsley, 1989), and for finite clauses in German, where the subject appears in the Mittelfeld, just like the complements and adjuncts of the verb (Kiss, 1995). Another example of the same valence/function mismatch is the analysis of subject-auxiliary inversion in Sag and Wasow (1999), where a lexical rule empties the auxiliary’s subject valence, which has the result of forcing the valence object corresponding to subject to appear as the first element of the COMPS list instead. This ensures that the subject will not be realized preverbally, but as the first “com- plement” following the auxiliary verb, which is the desired structure. It should be said that many analyses of this type are motivated primarily by word order considerations, and so a possible al- ternative approach would be to use surface linearization constraints, without actually modifying the basic syntactic structure via valence manipulation. After replacing SUBCAT by SUBJ, SPR, and COMPS, researchers soon realized that for the treatment of some phenomena (most notably Binding Theory), they still needed a single list encoding all of the arguments of a head. So the SUBCAT list was revived in the form of the ARG(UMENT)-ST(RUCTURE) list, with one crucial difference: while SUBCAT as a valence fea- ture recorded the level of syntactic saturation for each higher phrase in the tree, ARG-ST was introduced as a static representation of the dependents of the lexical head. In its original concep- tion, this information is only found in the representation of the lexical head (an object of type word). But a variety of recent work (for instance Przepiórkowski 2001) has argued that certain phenomena require that ARG-ST information also be visible on phrasal constituents projected from the head. In simple cases, the ARG-ST list is identified with the concatenation of SUBJ, SPR, and COMPS at the lexical level, i.e., before any valence requirements have been saturated. However, the lists in question do not always line up in this fashion and the possibility of mismatches gives rise to a number of analyses of otherwise puzzling phenomena. We will briefly discuss two of these here, pro-drop and argument realignments in Austronesian languages. The standard transformational approach to missing subjects in finite environments has been to posit a null pronoun (pro) that instantiates the syntactic subject position. In keeping with HPSG’s general avoidance of unpronounced syntactic material, we can instead analyze the un- expressed subject as an ARG-ST element that does not have a corresponding valence expression. The following example from Italian (1a) and the corresponding lexical description of the verb mangia illustrate this idea: (1) a. Mangia un gelato. eat.3SG a icecream ‘S/he is eating an icecream.’ b. ARG-ST hNP[3sg], NPi SUBJ hi COMPS hNPi 3 Dependencies in which the subject participates, such as binding or agreement, can be accommo- dated straightforwardly if they are described as referring to the least oblique ARG-ST element, rather than the value of SUBJ. A more radical mismatch between valence and argument structure has been proposed by Manning and Sag (1998) and Manning and Sag (1999) for the realization of arguments in Western Austronesian languages such as Toba Batak. In this language clause-initial verbs form a VP with the immediately following argument NP. In the case of active voice (AV) morphology, this NP has the status of non-subject, as evidenced by the fact that a reflexive in that position has to be bound by a later (“higher”) NP. The example in (2) can be analyzed exactly like the corresponding English sentence (apart from the position of the subject NP). In particular, AGR-ST is the concatenation of SUBJ and COMPS: (2) a. [Mang-ida diri-na] si John.