Vowel harmony: why Finnish endings change

Almost every Finnish suffix comes in two versions. Talossa (in the house) and tytössä (in the girl) use the same ending, but the vowel differs. Finnish vowels fall into groups that cannot be mixed in one word, and suffixes copy the group of the word they attach to. This is called vowel harmony.

The three groups

• Back vowels: a, o, u. Words with these take back suffixes (-ssa, -lla, -ko).
• Front vowels: ä, ö, y. Words with these take front suffixes (-ssä, -llä, -kö).
• Neutral vowels: e, i. These do not count on their own. A word with only e and i takes front suffixes.

A word belongs to the back group if it contains any back vowel, and to the front group otherwise.

Examples

Kieli (language) has only i and e, so it is a front word, and the suffix is -ssä. This is the case learners most often get wrong.

Common mistakes

• Mixing the groups. Wrong: talossä. Right: talossa. A back word with a front suffix is always wrong.
• Assuming the spelling decides it. Go by the vowels in the word, not by what it means. Kieli is a front word even though it sounds like a back word to many learners.
• Forgetting the stem changes. Harmony tells you which vowel to use, but some stems also change (lehti becomes lehde- before -ssä). Learn the stem with the word.

Why it helps

Once you know the group, you can predict the ending for almost any suffix. That is more useful than memorising each form separately, and it makes the case system much easier to learn.