Obligatory Contour Principle

In phonology, the Obligatory Contour Principle is a general principle stating that two identical features should not occur in succession.

Examples:

• A sequence of two identical vowels must either be broken up by hiatus or coalesce into a long vowel; they may not form a diphthong.
  • Similarly, diphthongs of the type /ij/ or /uw/ are practically unheard of; /ji/ and /wu/ are also prohibited by several languages, or at least do not contrast with /i/ and /u/ (English is one exception: cf. yeast vs. east)
• In tonal languages, adjacent syllables may not be marked for the same tone; in cases where this situation is found phonetically, it is analysed in terms of tone spreading, word tone or pitch accent.
• Languages commonly prohibit clusters of similar consonants, especially of two sibilants.

The OCP also accounts for the cross-linguistic rarity of roots containing several identical consonants (with the exception of baby-talk words such as mama, papa, nana, daddy, booboo, peepee, titty, which may fall under primitive reduplication).

The motivation of sound changes involving dissimilation may be included under the OCP.

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