If the stem ends in a consonant, an epenthetic /ə/ is inserted between the stem and this suffix: -о- if the final consonant of the stem is plain, and -е- if it's palatalized. For example:улав(ulav) —улавонь(ulavoń),марь(maŕ) —марень(mareń). If the stem ends in -й, this letter is replaced with -e-:ляй(läj) —ляень(läjeń). -ь is also replaced.
If the stem of a polysyllabic noun ends in -и or -ы, -e- (phonetically /jə/) is inserted between the stem and this suffix:маци(maci) —мациень(macijeń),шары(šarï) —шарыень(šarïjeń).
If the stem of a polysyllabic noun ends in -ю or -у, this suffix can be added directly to the stem, or to an epenthetic suffix-во-(-vo-):куцю(kuću) —куцюнь(kućuń) orкуцювонь(kućuvoń),келу(kelu) —келунь(keluń) orкелувонь(keluvoń).
If the stem ends in -а or -е, this suffix causes vowel alternation in shifting vowel-stem nominals such asшуфта(šufta) —шуфтонь(šuftoń),мокша(mokša) —мокшень(mokšeń),сельме(seľme) —сельмонь(seľmoń). In non-shifting vowel-stem nominals, there is no vowel alternation:мода(moda) —модань(modań),веле(vele) —велень(veleń),пря(prä) —прянь(präń).
Although genitive is an inflected form in its own right, when used as a stand-alone adjective or as an attributive noun, further inflection has been documented, see, for example,мокшень(mokšeń).
