ABSTRACT
The diphthong is a gliding sound in which the tongue starts in the position of one vowel and immediately leaves it to glide towards another vowel position by the most direct route, without any diminution and subsequent reinforcement of the breath force. Diphthongs are of two kinds, falling and rising. A falling diphthong has its greatest prominence at the beginning: it is a decrescendo diphthong. A rising diphthong has its greater prominence at the end: it is a crescendo diphthong. Falling diphthongs can be made by the tongue starting from any vowel position and moving towards any other position. Rising diphthongs usually start from a close or half-close position and glide to a more open one: they can be represented by the semi-vowels. The number of diphthongs in an African language is, as a rule, not very large, though most languages have a few.
