Allomorfism

Allomorfism refers to the study of allomorphs, the variant realizations of a single morpheme, and the rules that govern when each realization is used. An allomorph is a distinct phonological or orthographic form that encodes the same grammatical meaning; the underlying unit is a morpheme, while its surface shape changes across contexts. The phenomenon is usually called allomorphy, but some authors use allomorfism as well.

Allomorphs are typically conditioned by phonological context, neighboring sounds, or syntactic or morphological environment. For example, in English the plural suffix has three common allomorphs for the morpheme that marks plurality: [s] as in cats [kæts], [z] as in dogs [dɔɡz], and [ɪz] or [əz] as in horses or buses [ˈhɔːˌzɪz], [ˈbʌsɪz]. Another well-known case is the past tense morpheme in English, realized as [t], [d], or [ɪd] after voiceless, voiced, or alveolar stop contexts, respectively.

Allomorphy can be systematic, arising from phonological rules (phonology-driven allomorphs), or irregular, tied to historical changes or lexicalized forms. Some theories distinguish conditioned allomorphs from zero allomorphs, where a morpheme is realized without an overt form. The study of allomorfism intersects morphology, phonology, and historical linguistics, and it informs computational modeling, language description, and the analysis of word formation and inflectional systems.

See also: morpheme, allomorph, allomorphy, morphophonology, inflection.