Allomorphs of {-s} and {-ed}
The morpheme {-s} occurs while conjugating verbs, e.g. he speaks, she thinks, or when building the plural of nouns, e.g. books, birds, etc., or when forming the genitive of a word, e.g. the cow’s fur.
The morpheme {-ed} occurs in the past tense and the past participle of verbs, e.g. we looked, I have painted, or when building adjectives like annoyed, astonished, etc.
Depending on the environment of these morphemes, the pronunciation changes slightly. These variations are called allomorphs.
Allomorphs of {-s}:
/s/ after voiceless consonants except /s, ʃ, tʃ/, e.g. looks = /lʊks/
/z/ after voiced consonants and vowels except /z, ʒ, dʒ/, e.g. drums = /drʌmz/
/ɪz/ after /s, ʃ, tʃ, z, ʒ, dʒ/, e.g. freezes = /’fri:zɪz/
Allomorphs of {-ed}:
/t/ after voiceless consonants except /t/, e.g. looked = /lʊkt/
/d/ after voiced consonants and vowels except /d/, e.g. believed = /bɪ’liːvd/
/ɪd/ after /t, d/, e.g. created = /kri’eɪtɪd/ (only with regular verbs, NOT with verbs like <did, emptied, spelt> etc.)
These rules fall under the category of MORPHOPHONOLOGY which is a mixture of morphology (word parts) and phonology (pronunciation).
The rules presented here show us the concept of complementary distribution:
Complementary distribution:
If one allomorph occurs in a certain environment, the other possible allomorphs of one morpheme do not occur in this environment --> allomophs cannot occur in mutually exclusive contexts
