Morphemes are sometimes expressed by elements that are less than full segme
nts, and, in a given language, the position of these elements in a word may
vary. A recent analysis of these 'mobile morphemes ' claims that their dis
tribution is best explained in an optimality-theoretic framework that incor
porates a set of featural alignment constraints (Akinlabi 1996) This paper
argues that featural alignment plays no role in the realization of 'mobile
morphemes'. Instead, it recognizes a set of licensing constraints that expl
icitly identifies where featural exponents of such morphemes may appear in
a word. Crucially, these licensing constraints, unlike featural alignment,
are not morpheme-specific and therefore enjoy cross-linguistic support. Ana
lyses of Chaha labialization, Terena nasalization, High tone realization in
the Edoid associative construction and Southern Sami vowel lowering in ter
ms of licensing are shown to be superior to the alignment-theoretic ones on
both descriptive and explanatory grounds.