rule (n.)
A term used in LINGUISTICS, and especially in GENERATIVE GRAMMAR, to refer to a formal statement of correspondence between linguistic ELEMENTS or STRUCTURES. In the case of generative rules, there is more involved than a set of descriptive statements summarizing one’s observations; generative rules are predictive, expressing a hypothesis about the relationships between SENTENCES which will hold for the LANGUAGE as a whole, and which reflect the NATIVE-SPEAKER’s COMPETENCE. In the classical account, a grammar is seen as a set of REWRITE RULES which will generate all and only the grammatical sentences of a language. The rules may be subclassified in terms of the COMPONENTS of the grammar in which they appear (e.g. ‘phonological rules’, ‘syntactic rules’, ‘lexical rules’).
Several types of rules have been recognized. The most basic types are PHRASE-STRUCTURE rules, of the form X ⇒ Y, and TRANSFORMATIONAL rules, of the form A ⇒ B, where A and B are STRINGS of structural elements. In Syntactic Structures (1957) a distinction was made between OPTIONAL and OBLIGATORY rules. Other types of rule commonly cited include RECURSIVE, GLOBAL, MOVEMENT, READJUSTMENT, VARIABLE, lexical INSERTION and lexical REDUNDANCY rules. In some later MODELS of generative grammar, the notion of a rule schema is introduced. This is a means of specifying a set of rules without having to list them individually, e.g. S ⇒ Sn , where n refers to any number of sentences (greater than 1) that can be the result of this rule (as in CO-ORDINATE sentences, which may be of any length). In GENERALIZED PHRASE-STRUCTURE GRAMMAR, reference is made to IMMEDIATE DOMINANCE rules and LINEAR PRECEDENCE rules. In GOVERNMENT-BINDING THEORY there has been a shift away from the notion of rules to that of PRINCIPLES and PARAMETERS; in OPTIMALITY THEORY to the notion of CONSTRAINTS.
The linguistic sense thus contrasts with the traditional use of the term, where rules are recommendations for correct usage, as in ‘a preposition is not to be used at the end of a sentence’. No PRESCRIPTIVE or PROSCRIPTIVE implication is present in the linguistic sense of ‘rule’.
