From Wiktionary, the free dictionary
Nominals ending with ⟨ -si ⟩ , preceded by a vowel.
The inflectional stem replaces ⟨ -si ⟩ with ⟨ -te- ⟩ , which is subject to ⟨ t ⟩ → ⟨ d ⟩ consonant gradation. Before the plural marker ⟨ -i- ⟩ , the ⟨ -te- ⟩ reverts to ⟨ -s- ⟩ .
Partitive singular ending ⟨ -ta ⟩ /⟨ -tä ⟩ , partitive plural ending ⟨ -a ⟩ /⟨ -ä ⟩ and genitive plural ending ⟨ -en ⟩ .
back vowels (contains ⟨ a ⟩ , ⟨ o ⟩ or ⟨ u ⟩ )
front vowels (no ⟨ a ⟩ , ⟨ o ⟩ or ⟨ u ⟩ )
Consonant gradation detail [ edit ]
grade
t → d
nominative
–
käsi
genitive
weak
käd en
partitive
strong
kät tä
elative
weak
käd estä
illative
strong
kät een
Complete declension example highlighting consonant gradation (t → d)[ edit ]
{{fi-decl-käsi }}
See Finnish käsi-type nominals .