In contrast to popular approaches to syntax and parsing, VirtualWorks is strongly committed to the use of extremely large local grammar systems which can analyze substantial portions of natural language with a very high degree of accuracy.
Since we are still a far cry from a comprehensive and semantically realistic treatment of large fragments of any natural language, VirtualWorks aims rather at describing well-understood semantic subsets in a detailed way. This holds for the description of both argument and predicates. The latter express relations between arguments (VirtualWorks calls them “propositional forms”) and they come in a number of very different forms that are however rarely distinguished in other approaches to syntax.
Local grammars for propositional forms have the advantage that they identify the nature of the predicates by separate grammars for the different ways of expressing propositional forms (thereby also capturing the many variants of the same underlying propositional form). On the other hand, there are also very detailed grammars for the different types of argument structures involving such notions as persons, dates, organizations, locations and many others, each which requires a grammar specification of its own.
General rule based grammars that do not make such semantic distinctions from the beginning cannot capture the structure of utterances in a reliable way.