Editing Allomorph (section)

===Past tense allomorphs===
For example, an English past tense morpheme is ''-ed'', which occurs in several allomorphs depending on its phonological environment by assimilating the voicing of the previous segment or the [[epenthesis|insertion]] of a [[schwa]] after an [[alveolar stop]].<ref name=":02" /> A possible set of assimilations is:

* as {{IPA|[-əd]}} or {{IPA|[-ɪd]}} in verbs whose [[word stem|stem]] ends with the alveolar stops {{IPA|[t]}} or {{IPA|[d]}}, such as 'hunted' {{IPA|[hʌntɪd]}} or 'banded' {{IPA|[bændɪd]}}
* as {{IPA|[-t]}} in verbs whose stem ends with voiceless phonemes other than {{IPA|[t]}}, such as 'fished' {{IPA|[fɪʃt]}}
* as {{IPA|[-d]}} in verbs whose stem ends with voiced phonemes other than {{IPA|[d]}}, such as 'buzzed' {{IPA|[bʌzd]}}

The "other than" restrictions above are typical for allomorphy. If the allomorphy conditions are ordered from most restrictive (in this case, after an alveolar stop) to least restrictive, the first matching case usually has precedence. Thus, the above conditions could be rewritten as follows:

* as {{IPA|[-əd]}} or {{IPA|[-ɪd]}} when the stem ends with the alveolar stops {{IPA|[t]}} or {{IPA|[d]}}
* as {{IPA|[-t]}} when the stem ends with voiceless phonemes
* as {{IPA|[-d]}} elsewhere

The {{IPA|[-t]}} allomorph does not appear after stem-final {{IPA|/t/}} although the latter is voiceless, which is then explained by {{IPA|[-əd]}} appearing in that environment, together with the fact that the environments are ordered (that is, listed in order of priority). Likewise, the {{IPA|[-d]}} allomorph does not appear after stem-final {{IPA|[d]}} because the earlier clause for the {{IPA|/-əd/}} allomorph has priority. The {{IPA|/-d/}} allomorph does not appear after stem-final voiceless phoneme because the preceding clause for the {{IPA|[-t]}} comes first.

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 take priority over the general cases listed above.<ref name=":02" />