If an alternation is judged to be non-phonological, it must be interpreted either as morphophonemic - the covariants (or all but one of them) being assigned indexical signata - or as morphological, i.e. as a relative signans with a symbolic signatum.
- Andersen (2004), Pag. 421

In synchronic analysis it may be difficult to determine whether an alternation is to be interpreted as morphophonemic (the alternants are co-variants of absolute signantia) or morphological (the modification of the signans is in itself a signans).
- Andersen (2004), Pag. 400