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Allomorphy is the phenomenon that a morpheme has more than one phonetic form (Booij 2012;Rubach and Booij 2001). Allomorphy may be the effect of a phonological rule, for instance Final Devoicing, the constraint that requires obstruents in coda position to be voiceless. This constraint explains the variation in phonetic form of the morpheme hoed hat: in the singular noun hoed it has the phonetic form [hut], and in the plural form hoeden [hudən] it has the phonetic form [hud]. In many cases of allomorphy, both of stems and of affixes, the variation in phonetic form does not follow from a general phonological constraint. For instance, the prefix in- has allomorphs such as il- and ir- (compare inadequaat in-adequaat inadequate, illegaal il-legaal illegal, irrationeel ir-rationeel irrational), but there is no phonological constraint that excludes /n/ before /l/ or /r/, witness onlogisch on-logisch illogical and onredelijk on-redelijk irrational. The term 'allomorphy' is often used to exclusively refer to the latter type of allomorphy.


When allomorphy cannot be predicted from phonological constraints, the allomorphs cannot be derived from a common underlying form. Therefore, they must be listed individually in the grammar/lexicon. The selection of a particular allomorph from the set of allomorphs may be governed by phonological constraints. For instance, the selection of the suffix -aar in a word like wandelaar wandel-aar walker (instead of *wandel-er) follows from the constraint that sequences of syllables with schwa should be avoided if possible (Booij 1998).

The term ‘allomorph’ may also be used to refer to morphemes that have nothing in common phonologically, but have the same grammatical function. For instance, the suffixes -s and -en may be considered allomorphs of the grammatical morpheme PLURAL. However, it may be more appropriate in such cases to speak of competing affixes that compete for expressing the same information.            

Allomorphy may be governed by non-phonological factors, and may be a relic of the past. For instance, the form ziele /zilə/ soul of present-day Dutch ziel /zil/ is the older form that was used in the past to coin the compound zielenrust zielenrust /zilə-rʏst/ peace of mind (the e is spelled as <en> in present Dutch orthography). In jongensboek jongens-boek /jɔŋəns-buk/ boy’s book, the form jongens is used as it is the old genitive form of jongen /jɔŋə/ boy(see also Booij 1996).

See the following topics for more information:

  • Booij, Geert1996Verbindingsklanken in samenstellingen en de nieuwe spellingregelingNederlandse Taalkunde1126-134
  • Booij, Geert1998Prosodic output constraints in morphologyKehrein, Wolfgang & Wiese, Richard (eds.)Phonology and morphology of the Germanic languagesTübingenNiemeyer143-163
  • Booij, Geert2012Allomorphy and the architecture of grammarPhonological Explorations: Empirical, Theoretical, and Conceptual IssuesBerlin/New YorkDe Gruyter9-24
  • Rubach, Jerzy & Booij, Geert2001Allomorphy in Optimality Theory: Polish iotationLanguage7726-60