In
linguistics, an alternation is the phenomenon of a
morpheme exhibiting variation in its
phonological realization. Each of the various realizations is called an alternant. The variation may be conditioned by the phonological,
morphological, and/or
syntactic environment in which the morpheme finds itself.
Alternations provide linguists with data that allow them to determine the
allophones and
allomorphs of a language's phonemes and morphemes and to develop analyses determining the distribution of those allophones and allomorphs.
The term "sound change" refers to
diachronic changes, which occur in a language's sound system. On the other hand, "alternation" refers to changes that happen
synchronically (within the language of an individual speaker, depending on the neighbouring sounds) and do not change the language's
underlying system.
An example of a phonologically conditioned alternation is the
Englishplural marker commonly spelled s or es.[1] This morpheme is pronounced /s/, /z/, or /ᵻz/,[note 1] depending on the nature of the preceding sound.
If the preceding sound is a
sibilant consonant (one of /s/,/z/,/ʃ/,/ʒ/), or an
affricate (one of /tʃ/,/dʒ/), the plural marker takes the form /ᵻz/. Examples:
mass/ˈmæs/, plural masses/ˈmæsᵻz/
fez/ˈfɛz/, plural fezzes/ˈfɛzᵻz/
mesh/ˈmɛʃ/, plural meshes/ˈmɛʃᵻz/
mirage/mɪˈrɑːʒ/, plural mirages/mɪˈrɑːʒᵻz/
church/ˈtʃɜːrtʃ/, plural churches/ˈtʃɜːrtʃᵻz/
bridge/ˈbrɪdʒ/, plural bridges/ˈbrɪdʒᵻz/
Otherwise, if the preceding sound is
voiceless, the plural marker takes the likewise voiceless form /s/. Examples:
mop/ˈmɒp/, plural mops/ˈmɒps/
mat/ˈmæt/, plural mats/ˈmæts/
pack/ˈpæk/, plural packs/ˈpæks/
cough/ˈkɒf/, plural coughs/ˈkɒfs/
myth/ˈmɪθ/, plural myths/ˈmɪθs/
Otherwise, the preceding sound is voiced, and the plural marker takes the likewise voiced form /z/.
French has an example of morphologically conditioned alternation. The
feminine form of many
adjectives ends in a
consonant sound that is missing in the masculine form. In spelling, the feminine ends in a
silent e, while the masculine ends in a silent consonant letter:[2]
Syntactically conditioned alternations can be found in the
Insular Celtic languages, where words undergo various initial
consonant mutations depending on their syntactic position.[3] For example, in
Irish, an adjective undergoes
lenition after a feminine singular noun:
unmutated mórmˠoːɾˠ]'big', mutated in bean mhór[bʲanwoːɾˠ]'a big woman'
^The vowel of the inflectional suffix -⟨es⟩ may belong to the phoneme of either /ɪ/ or /ə/ depending on dialect, and ⟨ᵻ⟩ is a shorthand for "either /ɪ/ or /ə/". This usage of the symbol is borrowed from the Oxford English Dictionary.