Principle 3. Forms which have a common semantic distinctiveness but which differ in phonemic form in such a way that their distribution cannot be phonologically defined constitute a single morpheme if the forms are in complementary distribution in accordance with the following restrictions: (1) Occurrence in the same structural series has precedence over occurrence in different structural series in the determination of morphemic status. (2) Complementary distribution in different structural series constitutes a basis for combining possible allomorphs into one morpheme only if there also occurs in these different structural series a morpheme which belongs to the same distribution class as the allomorphic series in question and which itself has only one allomorph or phonologically defined allomorphs. (3) Immediate tactical environments have precedence over nonimmediate tactical environments in determining morphemic status. (4) Contrast in identical distributional environments may be treated as submorphemic if the difference in meaning of the allomorphs reflects the distribution of these forms.
- Nida (1949), a pag.41-42