On the relationship between lexical semantics and syntax for the inference of context-free grammars

Abstract

Context-free grammars cannot be identified in the limit from positive examples (Gold 1967), yet natural language gram-mars are more powerful than context-free grammars and hu-mans learn them with remarkable ease from positive exam-ples (Marcus 1993). Identifiability results for formal lan-guages ignore a potentially powerful source of information available to learners of natural languages, namely, meanings. This paper explores the learnability of syntax (i.e. context-free grammars) given positive examples and knowledge of lexical semantics, and the learnability of lexical semantics given knowledge of syntax. The long-term goal is to develop an approach to learning both syntax and semantics that boot-straps itself, using limited knowledge about syntax to infer additional knowledge about semantics, and limited knowl-edge about semantics to infer additional knowledge about syntax.