In English there are changes in consonants, vowels, and stress, insertions, and elisions; and many of these are conditioned only by the phonetic surroundings of the morphemes. An example is the possessive suffix, which is "-əz" (or "-tz") after a sibilant, "-z" after a voiced non-sibilant, "-s" after a voiceless nonsibilant. In the case cited the alternation is called regular.
- Swadesh & Voegelin (2004), Pag. 11