Optimality Theory (OT) is a theory of constraints and constraint ranking used within the field of linguistics and, more specifically, within phonology. The theory was developed in the early 90s by Alan Prince and Paul Smolensky. Since its introduction, Optimality Theory has been a topic of interest and has been constantly and continuously further developed. OT is now considered a prominent approach within phonological theory, specifically concerning transformations and the explanation of phonological processes. The techniques of Optimality Theory have more recently been used within the field of linguistics to explain both syntactic and semantic transformations and processes.
Prince and Smolenksy's introductory manuscript, entitled, "Optimality Theory: Constraint Interaction in Generative Grammar," outlines a system of interactive constraints. The system of constraints helps to explain how a speaker’s phonological processes generate or regulate output. Optimality theory is based on the idea that there is a set of constraints that are universal to all languages, and these constraints are ranked and are violable. The interaction of these constraints is what regulates output.
The two types of constraints are faithfulness and markedness. Faithfulness constraints regulate variation between input and output, and work to keep transformations as minimal as possible. In other words, phonological output should remain as faithful as possible to the input into the phonological system. Another critical aspect of Optimality Theory is that all constraints are violable, which is both essential and obvious due to the presence of faithfulness constraints.
Markedness constraints are constraints on phonological output and can affect anything vowel or syllable length, vowel insertion, and reduplication. It is worth noting that markedness constraints and their ranking can vary between dialects or even individual speakers. It is the interaction among constraints of these two categories that creates the ideal outline for a continuum guiding phonology.
There are two main principles within Optimality Theory. The first guideline is that the constraints are universal. In addition, all constraints are present in the grammar of every language. Using these two rules, it is possible to explain that the only difference among the world's languages is constraint ranking. Since its introduction, there has been considerable debate as to whether the supposed universality of constraints is feasible.
When evaluating a transformation or phonological process using optimality theory, a unique chart is used to identify the option that is optimal or most harmonious. Constraints are ranked in a hierarchy specific to a language, dialect, or speaker. Output is then evaluated using a simple measure or property known as minimal violation. The output that violates the least constraints is the winner or the optimal output.