Alternation (linguistics)

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.

Phonologically conditioned alternation

An example of a phonologically conditioned alternation is the English plural marker commonly spelled s or es. This morpheme is pronounced , , or , depending on the nature of the preceding sound.

1. If the preceding sound is a sibilant consonant (one of ), or an affricate (one of ), the plural marker takes the form . Examples:
   • mass , plural masses
   • fez , plural fezzes
   • mesh , plural meshes
   • mirage , plural mirages
   • church , plural churches
   • bridge , plural bridges
2. Otherwise, if the preceding sound is voiceless, the plural marker takes the likewise voiceless form . Examples:
   • mop , plural mops
   • mat , plural mats
   • pack , plural packs
   • cough , plural coughs
   • myth , plural myths
3. Otherwise, the preceding sound is voiced, and the plural marker takes the likewise voiced form .
   • dog , plural dogs
   • glove , plural gloves
   • ram , plural rams
   • doll , plural dolls
   • toe , plural toes