optimality theory (OT)

In PHONOLOGY, a theory developed in the early 1990s concerning the relationship between proposed underlying and output REPRESENTATIONS. In this approach, an INPUT representation is associated with a class of candidate OUTPUT representations, and various kinds of filter are used to evaluate these outputs and select the one which is ‘optimal’ (i.e. most well-formed). The selection takes place through the use of a set of well-formedness CONSTRAINTS, RANKED in a hierarchy of relevance on a language-particular basis, so that a lower-ranked constraint may be violated in order to satisfy a higher-ranked one. The candidate representation which best satisfies the ranked constraint hierarchy is the output form. For example, in English the negative prefix in- (e.g. insufficient) has two output forms, im- before bilabials (as in impossible, immodest), and in- elsewhere (inarticulate, involuntary, etc.). The coexistence of these forms means that there is conflict between the class of FAITHFULNESS constraints (which require identity between input and output) and the class of constraints which impose restrictions on possible sequences of sounds – in this case, a constraint requiring that adjacent CONSONANTS have identical place of articulation – which needs to be resolved by an appropriate ranking of the relevant constraints. Optimality theory thus aims to account for a wide range of phenomena by specifying the interaction of a small number of UNIVERSAL constraints, which apply variously across languages in producing phonological representations. A particular constraint may achieve high ranking in one language (i.e. its output accounts for many surface forms) and low ranking in another (i.e. its output accounts for only a small class of forms). Although initially developed in relation to phonology, during the later 1990s optimality theory came to be extended to MORPHOLOGY and SYNTAX.