Special Realizations of Morphemes: Allomorphs
Working through the section on phonetics and phonology you learn that the very rule that determines the phonetic form of the plural morpheme is a morphophonemic rule. This nomenclature makes perfectly sense as its application is not only pre-determined by the phonology but also by the morphology – both phonology and morphology interact. In short, morphophonemic rules specify the pronunciation of morphemes.
The reciprocity at work in morphophonemics may also be applied to analyze morphological phenomena in form ofallomorphs.
Allomorphs are concrete realizations of a morpheme. So, the phonetic realizations /id/, /d/ and /t/ are grouped together as allomorphs of the past tense morpheme -ed. Clearly, all three morphs are different phonetic variants; yet, all three alternate forms represent the same morpheme – namely, the English past tense.
Interestingly, the distribution of the three allomorphs of the productive English regular past tense morpheme is not a question of mere arbitrariness; instead, allomorphs are conditioned by different factors. The example above shows phonologically conditioned allomorphs: /id/ is used after the alveolar stops /t/ and /d/; voiced /d/, in contrast, is chosen after voiced segments other than /d/, and the voiceless /t/ occurs after voiceless consonants other than /t/.
In addition to the phonological conditioning, allomorphs can also be gramatically and lexically conditioned. If we take a look at the plural marker, we find that the most common form to produce a plural out of a singluar form is the suffixation of -s. However, if we take the noun "ox", its plural form is oxen, so the plural marker is -en. This plural marker is lexically conditioned as "oxen" is the only word in the English language with this particular plural form. Also, allomorphs can be gramatically conditioned. This occurs e.g. in the German language, when "adjectives change their form depending on the gender of the noun they modify" (Bauer 1988,14). Although these morphs are clearly separate, the realise the same morpheme.