metarule (n.)

A term used in LINGUISTIC theory to refer to a type of RULE which defines some rules in a GRAMMAR on the basis of the properties of others already present in the grammar. Metarules are particularly important in GENERALIZED PHRASE-STRUCTURE GRAMMAR, where they derive IMMEDIATE DOMINANCE rules from immediate dominance rules. They allow the capturing of certain GENERALIZATIONS which are handled by TRANSFORMATION in transformational grammar; for example, the relation between active and PASSIVE sentences is captured by a metarule deriving rules for passive VPs from rules for active VPs. Metarules, it has been said, in effect provide a grammar which can be used for generating a grammar – in other words, a METAGRAMMAR.