Optimality theory
Optimality Theory (frequently abbreviated OT; second word normally capitalized by convention) is a linguistic model proposing that the observed forms of language arise from the interaction between conflicting constraints. OT differs from other approaches to phonological analysis, such as autosegmental phonology and linear phonology (SPE), which typically use rules rather than constraints. OT models grammars as systems that provide mappings from inputs to outputs; typically, the inputs are conceived of as underlying representations, and the outputs as their surface realizations.
Theory
There are three basic components of the theory:
GEN takes an input, and generates the list of possible outputs, or candidates,
CON provides the criteria, in the form of strictly ordered violable constraints, used to decide between candidates, and
EVAL chooses the optimal candidate based on the constraints, and this candidate is the output.
Optimality theory assumes that these components are universal. Differences in grammars reflect different rankings of the universal constraint set, CON. Part of language acquisition can then be described as the process of adjusting the ranking of these constraints.