Morphemes often behave differently phonologically in ways that cannot be explained purely phonologically: one morpheme undergoes or triggers a process while another morpheme fails to undergo or trigger that process, even though the two are in all relevant respects indistinguishable. Piro syncope (Matteson 1965, Kisseberth 1970, Lin 1997) provides an example of such morpheme-specific phonology. Morphemes differ in whether they cause the preceding vowel to delete (/heta+nu/ [hetanu] Ogoing to seeP vs. /heta+lu/ [hetlu] Osee itP), and in whether they undergo deletion themselves (/meyi+wa+lu/ [meyiwlu] OcelebrationP vs. /heta+wa+lu/ [hetawalu] Ogoing to see him yetP). As the behavior of the homophonous pair of /-wa/ morphemes illustrates, morphemes that fail to condition syncope can differ in whether they undergo the process.
Pater, Joe, "The Locus of Exceptionality: Morpheme-Specific Phonology as Constraint Indexation" (2007). Linguistics Department Faculty Publication Series. 172.
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