binary feature

A property which can be used to classify linguistic UNITS in terms of two mutually exclusive possibilities, such as in PHONOLOGY the presence versus the absence of VOCAL FOLD vibration, or lip-ROUNDING. Binary features are a major organizational principle of DISTINCTIVE FEATURE theories of phonology, where it is conventional to mark the OPPOSITION using ± in square brackets; e.g. a sound is characterized as [+voice] or [−voice]. Binary features are also established in GRAMMATICAL and SEMANTIC analyses of LEXICAL ITEMS, within GENERATIVE grammar, where the same TRANSCRIPTIONAL convention is used, e.g. NOUNS have such properties as [+common], [−common]. Binary features stand in contrast to ‘unary’ and ‘multi-valued’ (‘n-valued’ or ‘n-ary’) features. For example, in ‘unary component theory’ in phonology, binary notions (e.g. [±round]) are replaced by single elements (e.g. [round]).