allomorph

Definition


An allomorph is one of two or more complementary morphs which manifest a morpheme in its different phonological or morphological environments.
Discussion


The allomorphs of a morpheme are derived from phonological rules and any morphophonemic rules that may apply to that morpheme.
Examples (English)


The plural morpheme in English, usually written as '-s', has at least three allomorphs:


* [-s] as in [hQts] 'hats'
* [-z] as in [d&u0254;gz] 'dogs'
* [«z] as in [bŒks«z] 'boxes'
(Hartmann, R.R.K., and F.C. Stork. 1972.Dictionary of language and linguistics. London: Applied Science.)

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:

* as /əd/ or /ɪd/ in verbs whose stem ends with the alveolar stops /t/ or /d/, such as 'hunted' /hʌntəd/ or 'banded' /bændəd/
* as /t/ in verbs whose stem ends with voiceless phonemes other than /t/, such as 'fished' /fɪʃt/
* as /d/ in verbs whose stem ends voiced phonemes other than /d/, such as 'buzzed' /bʌzd/

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:

* as /əd/ or /ɪd/ when the stem ends with the alveolar stops /t/ or /d/
* as /t/ when the stem ends with voiceless phonemes
* as /d/ elsewhere

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, like the verb "break"), which therefore take priority over the general cases listed above.