power (n.)

A term used in the formal evaluation of GRAMMARS, and particularly found in discussion of GENERATIVE theories; also called capacity. Basically, grammar A would be said to be more powerful than grammar B if it can generate more LANGUAGES (SENTENCES, etc.) than B. In this sense, a CONTEXT-free grammar is more powerful than a FINITE-STATE GRAMMAR. It is important, however, that a grammar should not become too powerful, in the sense that it generates sentences which are ungrammatical, structural descriptions which are intuitively implausible, or a characterization of natural language that is too broad (e.g. including features of non-language systems). FORMAL constraints therefore have to be built into grammatical MODELS to restrict the power of grammars in specific ways, and much current discussion is focused on this subject. A further distinction is often introduced, between weak and strong generative power within a grammar. In the notion of ‘weak’ generative power, a grammar (or RULE, or set of rules, etc.) is said to be more powerful than another if it GENERATES more grammatical sentences. In the notion of ‘strong’ generative power, a grammar is said to be more powerful if it assigns to these sentences a set of STRUCTURAL DESCRIPTIONS which more satisfactorily shows their relationships.