Allomorph

In linguistics, an allomorph is a variant form of a morpheme, that is, when a unit of meaning varies in sound without changing meaning. The term allomorph explains the comprehension of phonological variations for specific morphemes.

English has several morphemes that vary in sound but not in meaning. Examples include the past tense and the plural morphemes.

For example, in English, a past tense morpheme is -ed. It occurs in several allomorphs depending on its phonological environment, assimilating voicing of the previous segment or inserting a schwa when following an alveolar stop:

Notice the "other than" restrictions above. This is a common fact about allomorphy: if the allomorphy conditions are ordered from most restrictive (in this case, after an alveolar stop) to least restrictive, then the first matching case usually "wins". Thus, the above conditions could be re-written as follows:

The fact that the /t/ allomorph does not appear after stem-final /t/, despite the fact that the latter is voiceless, is then explained by the fact that /əd/ appears in that environment, together with the fact that the environments are ordered. Likewise, the fact that the /d/ allomorph does not appear after stem-final /d/ is because the earlier clause for the /əd/ allomorph takes priority; and the fact that the /d/ allomorph does not appear after stem-final voiceless phonemes is because the preceding clause for the /t/ takes priority.

Irregular past tense forms, such as "broke" or "was/ were", can be seen as still more specific cases (since they are confined to certain lexical items, such as the verb "break"), which therefore take priority over the general cases listed above.

Allomorphy can also exist in stems or roots, as in Classical Sanskrit:

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