Principle 3. Forms which possess a common semantic distinctiveness, but which differ in their phonemic form in such a way that the distribution of the forms cannot be phonologically defined, constitute a single morpheme if the forms are in complementary distribution, subject to the following restrictions: (1) [...] Complementary distribution in tactically different environments constitutes a basis for combining different forms into one morpheme only on the following condition: that some other morpheme - belonging to the same distribution-class, and having either a single phonemic shape or phonologically defined alternant shapes - occurs in all the tactically different environment where the forms in question are found. (2) In determining the morphemic status of forms, tactically identical environments takes precedence over the larger (non-immediate) tactical environment. (3) In determining the morphemic status of forms, the immediate tactical environment take precedence over tactically different environments. (4) Different forms that contrast in identical distributional environments may neverless be assigned to the same morpheme, if the difference in meaning between them is identical with the difference in meaning derived from the distribution of the related forms.
- Nida (1948), a pag.421-422