Deterministic Parsing and Unbounded Dependencies

DETERMINISTIC PARSING AND UNBOUNDED DEPENDENCIES Ted Briscoe Dept of Linguistics, Lancaster University Bailrigg, Lancashire LA1 4YT, UK ABSTRACT This paper assesses two new approaches to deterministic parsing with respect to the analysis of unbounded dependencies (UDs). UDs in English are highly locally (and often globally) ambiguous. Several researchers have argued that the difficulty of UDs undermines the programme of deterministic parsing. However, their conclusion is based on critiques of various versions of the Marcus parser which represents only one of many possible approaches to deterministic parsing. We examine the predictions made by a LR(1) deterministic parser and the Lexicat deterministic parser concerning the analysis of UDs. The LR(1) technique is powerful enough to resolve the local ambiguities we examine. However, the Lexicat model provides a more psychologically plausible account of the parsing of UDs, which also offers a unified account of the resolution of local and global ambiguities in these constructions. INTRODUCTION Church (1980:117) and Johnson-Laird (1983:313) have argued that the high degree of ambiguity in unbounded dependencies undermines the programme of deterministic parsing. Their conclusion is based on critiques of various versions of the Marcus parser (Marcus, 1980; Berwick & Weinberg, 1984). This parser represents only one of many possible approaches to deterministic parsing.. Therefore, the conclusion that deterministic parsing, m general, is impractical or psychologically implausible may be premature. In the next section, we outline the problems for the deterministic analysis of unbounded dependencies. In the succeeding sections, we present two alternative parsing techniques (and associated grammars) which make differing predictions concerning the onset and location of indeterminacy in the analysis of unbounded dependencies. We argue that the LR(1) parser is capable of deterministically resolving the local ambiguities which occur in these constructions, whilst the Lexicat parser is not. In the final section, we evaluate these predictions in the light of the Determinism Hypothesis (Marcus, 1980) and the Interactive Determinism Hypothesis (Briscoe & Boguraev, 1984; Briscoe, in press) and argue that the Lexicat parser in conjunction with the Interactive Determinism Hypothesis provides the most psychologically plausible and unified account of the parsing of unbounded dependencies. UNBOUNDED DEPENDENCY AMBIGUITIES Unbounded dependencies are found in English constituent questions, relative clauses and topicalised constructions. The dependency is between the preposed constituent and its point of attachment. For example, in (1) Who is preposed and functioning as direct object of the transitive verb like. (I) Who do you like _e Most current theories of grammar represent the grammatical role of the prcposcd constituent by associating it with the normal position of a constituent having that grammatical role. In several theories, this position is occupied by a phonologically null category or trace which is grammatically linked to the prcposed constituent. Wc will use _e to mark this position because each of the grammars associated with the parsers we consider adopts a 'positional' account of the recovery of the grammatical role of the preposed constituent. However, we use _c to mark an unambiguous point of attachment without any commitment to the presence of phonologically …

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