equivalence (n.)

A relationship of equality of POWER between GRAMMARS. Grammars which GENERATE the same set of SENTENCES are said to be equivalent or weakly equivalent. Grammars which generate the same set of PHRASE-MARKERS are strongly equivalent, i.e. they generate not only the same sentences but assign the same STRUCTURAL DESCRIPTIONS to each. Grammars which display differences in the LABELLING or BRACKETING of structures, or which generate different sets of sentences, are said to be non-equivalent. The term is also used in other SYNTACTIC and SEMANTIC contexts, e.g. ‘DISTRIBUTIONAL equivalence’ (between units with the same distribution), ‘semantic equivalence’ (i.e. SYNONYMY).