The morphemes of the corpus may be listed under their classes in a morpheme index. Such an index is useful as stating the morpheme stock of the language, and the status that each has in the morphology (indicated by the class in which the morpheme is contained). If the classes are mutually exclusive as to morphemes […] each morpheme would be listed only once.
- Harris (1951), Pag. 252

The classes of 15.3 [Procedure: Rough Similarity of Environments] are mutually exclusive in respect to morphemes. If a morpheme is a member of a particular class, which may be included in a particular general class, it is not a member of any other class.
- Harris (1951), Pag. 257

The morpheme class environments of the resultant classes of chapter 15, say 'N' and 'V', are necessarily mutually exclusive. For let us suppose that in a particular environment 'A' a sequence 'XY' had equalled both 'N' and 'V'. Then 'AXY = A N = A V', and only one of these, either 'A N' or 'A V' would have been the resultant […]. However, there may be cases of morphemes or segment variants of morphemic units in two distinct classes having identical phonemic forms, so that in particular utterances the phonemic environment of 'N' and that of 'V' may be identical. E.g. /yur in./ is I '-Na = A' plus 'N' as an answer to 'Where shall we go to ?' ('your inn.'), but 'I = N' plus 'V' plus 'P' as an answer to 'How did I make out?' ('You’re in.').
- Harris (1951), Pag. 296, n.69