Replacive Morphemes
Another analytical perspective on sound alternations treats the phenomena not as merely alternation but rather a "replacive" morpheme that replaces part of a word. In this analysis, the alternation between goose/geese may be thought of as goose being the basic form where -ee- is a replacive morpheme that is substituted for oo.
- goose → g-ee-se
This usage of the term morpheme (which is actually describing a replacement process, and not a true morpheme), however, is more in keeping with Item-and-Process models of morphology instead of Item-and-Arrangement models.
Read more about this topic: Apophony