Example
The English plural morpheme for nouns has three allomorphs:
(notation in SAMPA)
from: Iggy Roca and Wyn Johnson, a course in phonology, Blackwell, 1999; p. 621
... reduplication. Also extremely common is vowel gradation; every root has (not necessarily all distinct) zero, guna[?], and vrdhii[?] grades. If V is the vowel of th ...