In many languages all the members of one class may have in common some phonemic feature which is absent in all the members of other classes. Thus in Semitic languages all morphemes of class 'C' […] consist of several consonants, usually three and almost always interrupted; all the morphemes of classes 'B', 'C' consist of an interrupted sequence of vowels, rarely with a consonant added. In Tonkawa, verb-theme morphemes are bound, noun-theme morphemes free. These differences may be such as appear only in certain environments of the class. There may be differences in contours, in phonemic junctures, or in morphophonemes. In any case, it is useful to state all such correlations. We may say that these phonemic characteristics of a class have a meaning, as indicating that class of morphemes. The considerations may have led us to include phonemically identical morphemes in various classes.
- Harris (1951), a pag.261