Parsing with Principles and Probabilities

This paper is an attempt to bring together two approaches to language analysis. The possible use of probabilistic information in principle-based grammars and parsers is considered, including discussion on some theoretical and computational problems that arise. Finally a partial implementation of these ideas is presented, along with some preliminary results from testing on a small set of sentences. I n t r o d u c t i o n Both principle-based parsing and probabilistic methods for the analysis of natural language have become popular in the last decade. While the former borrows from advanced linguistic specifications of syntax, the latter has been more concerned with extracting distributional regularities from language to aid the implementation of NLP systems and the analysis of corpora. These symbolic and statistical approaches axe beginning to draw together as it becomes clear that one cannot exist entirely without the other: the knowledge of language posited over the years by theoretical linguists has been useful in constraining and guiding statistical approaches, and the corpora now available to linguists have resurrected the desire to account for real language data in a more principled way than had previously been attempted. This paper falls directly between these approaches, using statistical information derived from corpora analysis to weight syntactic analyses produced by a 'principles and parameters' parser. The use of probabilistic information in principle-based grammars and parsers is considered, including discussion on some theoretical and computational problems that arise. Finally a paxtial implementation of these ideas is presented, along with some preliminary results from testing on a small set of sentences. G o v e r n m e n t . B i n d i n g T h e o r y The principles and paxameters paradigm in linguistics is most fully realised in the Government-Binding Theory (GB) of Chomsky [Chomsky1981, Chomsky19861 and others. The grammar is divided into modules which M a t t h e w C r o c k e r Centre for Cognitive Science University of Edinburgh