Traditional natural language parsers are based on rewrite rule systems developed in an arduous, time-consuming manner by grammarians. Most of the grammarian's work is devoted to the disambiguation process, first hypothesizing rules which dictate constituent categories and relationships among words in ambiguous sentences, and then seeking exceptions and corrections to these rules. This grammar refinement process is time-consuming and difficult, and has not yet resulted in a grammar which can be used by a parser to analyze accurately a large corpus of unrestricted text.