In general, the setting up of such new morphophonemic elements will be easier, the greater the phonemic similarity among the members of a morpheme. And over the whole corpus, if more of the morphemes have, in identical environments, identical alternations among their members, fewer morphophonemic elements will be set up; for then the morphophonemic set up for one morpheme will also serve for many other morphemes. It is therefore important to discover which alternations occur in many morphemes.
- Harris (1951), a pag.219