| Sg | Pl | |
| Nom | nauðsyn | nauðsynar (rule) |
| Acc | nauðsyn (rule) | nauðsynar (rule) |
| Dat | nauðsyn (rule) | nauðsynum (rule) |
| Gen | nauðsynar (rule) | nauðsyna (rule) |
| Sg | Pl | |
| Nom | nauðsynin (rule) | nauðsynarnar (rule) |
| Acc | nauðsynina (rule) | nauðsynarnar (rule) |
| Dat | nauðsyninni (rule) | nauðsynunum (rule) |
| Gen | nauðsynarinnar (rule) | nauðsynanna (rule) |