obligatory contour principle (OCP)

In some models of GENERATIVE PHONOLOGY, a principle which disallows adjacent identical elements in a REPRESENTATION. It was originally proposed for TONE languages, where it excluded sequences of identical adjacent tones (e.g. a sequence of High–High–Low would simplify to High–Low). The principle was later extended to SEGMENTAL phonology, especially in NON-LINEAR models, where it disallows any two identical FEATURES or NODES which are adjacent on a given TIER. Violations of this principle are handled through various processes, such as DISSIMILATION or the insertion of an EPENTHETIC vowel (as in the vowel which separates a sequence of TWO CORONAL SIBILANTS in such English plural forms as buses).