[...] the participial suffixes /-n/ and /-d/ are neverless allomorph [...] The allomorph /-d/ is productive: its potential distribution is not arbitrarily fixed like that of /-n/. Both allomorphs may occur in the same person's speech, but /-d/ occurs in more colloquial socio-linguistics environments. On the other hand, /-n/ has a fixed distribution, but within this fixed range of occurrence the /-n/ may be said to have greater 'socio-linguistic acceptability'. This facts are synchronic as well as diachronic; they apply to the present functioning of the language.
- Nida (1948), Pag. 432