In describing and identifying morphemic alternants (allomorphs) is frequently convenient to distinguish two types: basic and non-basic. This distinction may include phonologically defined allomorphs or morphologically defined allomorphs or both. [...] it is possible to select one alternant as basic and the others as [...] 'derived'. There are three types of criteria, in the following order of importance: (1) parallel structure, (2) general patterns of morphophonemic change, and (3) limitation of distribution.
- Nida (1948), a pag.426