抄録
Nilo-Saharan languages have relatively simple consonantal systems. For example, the consonantal system of Nilotic languages comprises voiceless and voiced stops, and nasals at five points of articulation - bilabial, dental, alveolar, palatal, and velar. In addition, Nilotic languages have one or two fricatives (f, s), a lateral (l), a trill (r), and two semi-vowels (w, y). Southern and eastern Nilotic languages developed tonal systems in compensation for the loss of the distinctive opposition between voiceless and voiced stops. A characteristic feature of the Nilotic consonantal system is a consonant alternation in which voiceless stops alternate with voiced stops, stops alternate with fricatives, and simple stops alternate with reduplicative stops morphophonologically. Most Nilo-Saharan languages show 5×2 vowel systems, which are structured into tongue-root-position-based vowel harmony systems of the "cross-height" type. Some languages lost [+ATR] /a/. Others lost [-ATR] /i/ and /u/.
