Most nominals with a basic form ending in -i do not have a separate inflectional stem, but endings are attached directly to the basic form itself:
Nominative sing.: tunti
Genitive: tunni/n
Possesive: tunti/mme
Partitive sing. tunti/a
There are three kinds of nominals with a basic form ending in -i, all with an inflectional stem in -e. The first group, words like kivi, which also form the partitive singular from this inflectional stem:
Nominative sing.: kivi
Genitive: kive/n
Posessive: kive/mme
Partitive sing.: kive/ä
Words like kivi thus form their partitive singular from an inflectional stem in -e, and differ in precisely this respect from words of the kieli type.
Kieli type nominals only differ from the kivi type in the partitive singular, where the -e- of the inflectional stem is dropped if the preceding consonant is l, r, or n; or t occurring after these or after a vowel:
Nominative: kieli
Genitive: kiele/n
Possesive: kiele/ni
Partitive: kiel/tä
A comparison of the tunti and kivi types shows that it is not possible to derive a rule from the basic form which would determine which nominals have an inflectional stem in -e and which do not... or is it?
Anyway, it is possible to state a rule operating in the opposite direction.
Nominals with an inflectional stem ending in short -e have a basic form ending in short -i.
This rule always allows us to derive the basic form from the inflectional stem.
The rule does not cover nominals with an inflectional stem in long -ee, such as perhe ‘family’, perhee/n, although there are a few exceptions: kolme ‘three’, kolme/n; itse ‘self’, itse/n; nalle ‘teddy’, nalle/n; nukke‘doll’, nuke/n.