Definition:
Morphophonology is the study of the phonological processes that operate at the juncture of morphemes — explaining why the same underlying morpheme surfaces with different phonological forms depending on the sounds surrounding it. The English plural morpheme is the classic example: spelled as -s or -es, it is pronounced /s/ after voiceless consonants (cats), /z/ after voiced sounds (dogs, trees), and /ɪz/ after sibilants (buses, churches). These are not random — they follow the same systematic rule applying across the lexicon. Morphophonology sits at the interface of morphology and phonology, and understanding it is essential for analyzing agreement, inflection, and derivational processes across languages.
In-Depth Explanation
Morphophonological alternations arise whenever morpheme combination triggers phonological processes — assimilation, deletion, insertion, or vowel change.
Allomorphs
An allomorph is a variant form of a morpheme. The English indefinite article has two allomorphs: a (before consonants) and an (before vowels). The English past-tense morpheme /-d/ surfaces as /t/ after voiceless consonants (walked → /wɔːkt/), /d/ after voiced sounds (jogged → /dʒɒgd/), and /ɪd/ after alveolar stops (wanted → /wɒntɪd/).
These alternations are phonologically conditioned — the selection of the allomorph is determined by the phonological environment, not by lexical choice.
Key Morphophonological Processes
Assimilation: A segment takes on features of an adjacent segment. English negative prefix in- becomes im- before bilabials (impossible), ir- before rhotics (irregular), il- before laterals (illegal).
Vowel alternation (ablaut): In Germanic languages, internal vowel change marks tense or number — English strong verbs (sing/sang/sung, foot/feet). These are non-concatenative morphological processes.
Epenthesis: Insertion of a segment to break up illegal consonant clusters. The plural /ɪz/ insertion in buses prevents an illegal sibilant-sibilant cluster.
Deletion: In casual speech, morpheme-final sounds may delete — English and → /ən/ in connected speech.
Japanese Morphophonology: Rendaku
Japanese rendaku (連濁) — sequential voicing — is a key morphophonological process in compound formation. The initial consonant of the second element in a compound may voice: hana (flower) + bi (fire) → hanabi (fireworks), but chi (blood) + shio (tide) → chishio (not chijio). Lyman’s Law governs the exceptions: rendaku does not apply if the second element already contains a voiced obstruent.
In SLA
L2 learners must acquire the morphophonological rules of the target language, which differ from L1 rules. Japanese learners of English must acquire the three-way allomorphy of the English plural; English learners of Japanese must internalize rendaku conditioning. These alternations are often not explicitly taught, requiring learners to abstract the pattern from input.
Common Misconceptions
“Morphophonology is just irregular spelling.” Apparent spelling irregularities often reflect underlying morphophonological regularities — the -es plural suffix and the /-ɪz/ allomorph reflect a phonological rule, not lexical exceptions.
“These alternations must be memorized individually.” Most allomorphic alternations follow general phonological rules. Learners who internalize the rule (rather than memorizing each form) handle novel words correctly, as demonstrated in wug tests.