Since Jakobson's (1948) analysis of Russian verbs as having one stem rather than two, it has been an attempt of generative phonology to minimize distinctly listed allomorphs in favor of phonological rules, some of which may be morphologically specific. Nonetheless there are certain allomorphs that cannot be derived one from the other, leading to “multiple URs” for the same morphemic category, such as the Moroccan 3rd person object clitic, which varies between the allomorphs ‐
h
(chosen after vowel‐final stems) and ‐
u
(chosen after consonant‐final stems), as will be discussed in §1.3 below. Such cases require distinct suppletive allomorphs, whose distribution is determined according to their phonological environments. The division of labor in dealing with allomorphy, then, is taken up both by purely phonological rules (such as those responsible for the voicing alternations of the English plural morpheme) and by morphological selection among separately listed allomorphs competing for insertion. In this chapter, we focus on the latter type of alternation between morphemes, while emphasizing that many cases of allomorphy not included in the present discussion are still best handled by phonological derivations from a single underlying form.