Two‐level representations for natural language

Abstract

Abstract For a number of years, transformational grammars have been extra‐ordinarily successful as models of natural language. Nevertheless, there has emerged a body of criticism based partly on formal as well as on practical considerations. As to the formal criticism, it emphasizes mathematical results which suggest that reliance on a transformational component might well be unnecessary. On the other hand, the more practical line of argument emphasizes the need for improved models of language from the standpoint both of performance as well as computational adequacy. The emphasis in this paper is directed toward the importance of two‐level grammars as a formal alternative. Two‐level grammars have an advantage in that each level in the grammar can be written in what appears to be a context free form. Even so, two‐level grammars have a generative capacity that is equivalent to that of a transformational grammar. After reviewing some mathematical preliminaries, a number of example grammars are introduced for describing particular constructions in the English language. In a forthcoming paper, some additional results will be discussed concerning the use of two‐level grammars in designing more effective parsers for natural language.