The same morpheme may have more than one form. Allomorphs variant forms of the same morpheme. Allomorphs whose relation is predictable by phonology are derived from a single underlying representation (ur) by phonological rules. The allomorphs [-s] and [- z] are derived by the rules: devoicing rule, obstruents become voiceless after voiceless obstruents in the same syllable, epenthesis rule, a schwa is inserted between two strident consonants in the same syllable. Recall that last week we determined that the definite article in arabic has the phonemic form / al-/, with all other allomorphs derived by a rule referring to the place of articulation of the following consonant. Use that rule to produce definite forms of the following nouns. So far we have been examining mostly alternations in affixes (e. g. arabic definite article, english plurals and past tense). Stems, however, can also exhibit alternations (recall [p m t]~[p m -] in permit, permission): selayarese stem allomorphy.