The role of rhythm in Kumam morphophonology

The Kumam (a western Nilotic) language is characterized by a trochaic rhythm in sentence-final or clause-final position. That is to say, penultimate syllables are pronounced long, while ultimate syllables are pronounced short at an end of a sentence or a clause. The penultimate syllables lengthened by the constraint of rhythm are phonetically long in sentence-final or clause-final position. The constraint of rhythm is not only phonetic but also phonemic. For instance, transitive infinitive forms of Kumam verbs are derived by adding a suffix -nç to the stem. The alveolar nasal consonant of the suffix is assimilated with the preceding consonant. One of the consonants is dropped at the boundary between the verb stem and the suffix. Stem vowels are lengthened in compensation for the loss of the consonant. In the case of the verbal stem which ends in a vowel, there is no consonant to be dropped. The compensatory lengthening of vowels is not supposed to take place when the verbal stem ends in a vowel. Nevertheless the stem vowels are lengthened because of the constraint of rhythm. The stem vowels are lengthened for adjustment to make a trochaic rhythm. The syllables lengthened through morphophonological processes are phonemically long. They keep their length in any environment. Output form in the verbal morphophonology (transitive infinitive forms, middle forms) and the nominal morphophonology (possessive constructions) are subject to the constraint of the rhythm in Kumam