(3) No change of consonants takes place in the root.
(4) The genitive plur. is found ending in -iden or -itten, before which the last vowel of the root is rejected by rule [3] or [4].
(5) Monosyllabic roots form the illative in h—n, the last vowel of the root being between the two consonants: täi, täihin; jää, jäähän. But dissyllables ending in a long vowel, e.g. harmaa, ehtoo, have the illative sing. in -sen and the illative plur. in -sin or -hin. Sing. harmaasen, plur. harmaisin or harmaihin.
Example of a noun of first declension with a hard vowel. Puu, a tree:—
| Sing. | Plur. | |
|---|---|---|
| Nom. | puu | puut |
| Part. | puuta | puita |
| Gen. | puun | puiden or puitten |
| In. | puussa | puissa |
| El. | puusta | puista |
| Il. | puuhun | puihin |
| Ad. | puulla | puilla |
| Abl. | puulta | puilta |
| All. | puulle | puille |
| Abes. | puutta | puitta |
| Prol. | [puutse] | puitse |
| Transl. | puuksi | puiksi |
| Ess. | puuna | puina |
| Com. | (puune) | puine |
| Instr. | (puun) | puin |
There is nothing to be remarked on the declension of this word, except that in the plur. the diphthong uu is shortened to u before the vowel i; puissa, etc., and not puuissa.
The declension of a noun with a soft vowel, e.g. työ, work, is exactly analogous, except that the suffixes have the soft forms -ssä, -stä, etc.
According to rule [4] before the i of the plural the vowel y is rejected from the diphthong yö. So suo, yö, tie form in the plural soissa, öillä, tein.