Allomorph
An allomorph is a phonological variant of a single morpheme, conditioned by the surrounding phonological or morphological environment. The morpheme is the abstract unit; the allomorphs are its surface realisations (Aronoff & Fudeman 2011; Haspelmath & Sims 2010).
The English plural morpheme has three allomorphs: [s], [z], and [ɪz]. All three carry the same meaning (plural number) but appear in complementary phonological contexts. Speakers select the right one automatically without any conscious rule, the same way they select the right phoneme in any spoken word.
The English Plural as a Standard Example
The plural morpheme illustrates phonologically conditioned allomorphy cleanly.
| Allomorph | Environment | Examples |
|---|---|---|
| [ɪz] / [əz] | After sibilants /s, z, ʃ, ʒ, tʃ, dʒ/ | buses, roses, bushes, garages, churches, judges |
| [s] | After voiceless non-sibilants /p, t, k, f, θ/ | cups, cats, books, cliffs, myths |
| [z] | After voiced non-sibilants and vowels | dogs, beds, balls, bees, shoes |
The same three-way pattern applies to the possessive -'s (the cat's, the dog's, the church's) and to the third-person singular present -s (walks, runs, watches). Three different morphemes, the same allomorphic distribution, all driven by the same phonological logic of voicing assimilation and sibilant epenthesis.
Past Tense -ed
The English regular past tense suffix shows parallel three-way allomorphy.
| Allomorph | Environment | Examples |
|---|---|---|
| [ɪd] / [əd] | After /t/ or /d/ | wanted, needed, decided |
| [t] | After voiceless non-coronal | walked, kissed, laughed |
| [d] | After voiced non-coronal and vowels | played, called, loved |
Phonological vs Morphological Conditioning
Allomorphy comes in two flavours.
Phonologically conditioned: the allomorph chosen depends on adjacent sounds. The plural and past-tense alternations above are phonologically conditioned, predictable from the rules of English phonotactics.
Morphologically conditioned: the allomorph chosen depends on the specific morpheme it attaches to, with no phonological motivation. The English plural also has unpredictable morphologically conditioned allomorphs: children (not *childs), oxen (not *oxes), feet (not *foots), mice, geese, sheep (zero-marked). The negative prefix in- surfaces as im- before bilabials (impossible), il- before /l/ (illegal), ir- before /r/ (irregular), in- elsewhere (incorrect), but the related un- shows no such alternation. The choice between in- and un- itself is morphologically conditioned: unable but inability.
Suppletion
When two allomorphs share no phonological material, the alternation is called suppletion. English shows suppletion in go / went (past tense), good / better / best (comparative and superlative), be / am / is / are / was / were (present and past). Suppletive allomorphs are historical accidents from competing source words; speakers learn them as paired entries rather than deriving them by rule.
Why Allomorphy Matters
Allomorphy is what makes the morpheme a useful abstraction. If every variant were treated as a separate unit, cats, dogs, buses would contain three different "plural morphemes." Treating them as allomorphs of a single morpheme captures the obvious generalisation that they all signal plurality and that the choice of variant is predictable from context.
Teaching Implications
The three allomorphs of -s and -ed are foundational pronunciation content for ELT. Many L2 learners produce only one variant (typically [s] for plural and [d] for past), which causes intelligibility issues for sibilant-final and voiceless-final stems: *buss for buses, *walkd for walked. Practical activities include sorting tasks (group nouns or verbs by which allomorph appears), minimal triplet work (cups / cubs / busses), and contrastive drills focused on the [ɪd] / [t] / [d] distribution. Recognition is also important for listening: learners who expect a single pronunciation may miss the inflection entirely when it surfaces as the [ɪz] or [ɪd] allomorph in connected speech. The morphologically conditioned cases (irregular plurals, suppletive verbs) need separate vocabulary-style treatment, since no rule predicts them.
References
- Aronoff, M., & Fudeman, K. (2011). What is Morphology? (2nd ed.). Oxford: Wiley-Blackwell.
- Haspelmath, M., & Sims, A. D. (2010). Understanding Morphology (2nd ed.). London: Hodder Education.
- Plag, I. (2003). Word-Formation in English. Cambridge: Cambridge University Press.
- Crystal, D. (2003). The Cambridge Encyclopedia of the English Language (2nd ed.). Cambridge: Cambridge University Press.