If you learn one structural fact about Finnish plurals, learn this one. The -t ending you met for talot ("houses") works in the nominative only. As soon as you need any other case — in the houses, from the houses, onto the houses — Finnish drops -t and marks the plural with a small -i- wedged between the stem and the case ending. This -i- is the real workhorse of the plural system: it carries plurality across the twelve remaining cases, while -t handles just one. Getting this division clear is the difference between guessing at plurals and building them reliably.
The mechanism: stem + -i- + case ending
An oblique (non-nominative) plural has three layers: the vowel stem, the plural -i-, and the case ending. Take talo:
| Case | Singular | Plural | Layers |
|---|---|---|---|
| inessive (in) | talossa | taloissa | talo + i + ssa |
| elative (from inside) | talosta | taloista | talo + i + sta |
| adessive (at/on) | talolla | taloilla | talo + i + lla |
| ablative (from on) | talolta | taloilta | talo + i + lta |
| allative (onto/to) | talolle | taloille | talo + i + lle |
The pattern is mechanical: whatever the singular ending is, the plural is the same ending with -i- in front of it. Learn talossa → taloissa once and you can generate taloista, taloilla, taloille on demand.
Näissä taloissa asuu enimmäkseen opiskelijoita.
Mostly students live in these houses.
Sain kirjeitä monilta vanhoilta ystäviltä.
I got letters from many old friends.
Panin avaimet pöydille eteisessä.
I put the keys on the tables in the hallway.
The minimal pair that makes it click
The clearest way to feel what -i- does is to put the singular and plural side by side. They differ by exactly one letter — the -i-:
| Singular | Plural | Meaning |
|---|---|---|
| talossa | taloissa | in the house → in the houses |
| talolla | taloilla | at the house → at the houses |
| talolle | taloille | to the house → to the houses |
That one letter is the entire signal of plurality. Miss it and you have said "in the house" when you meant "in the houses" — a real ambiguity, because Finnish has no article and no other clue to number in these cases.
Kissa nukkuu sohvalla.
The cat is sleeping on the sofa.
Kissat nukkuvat sohvilla.
The cats are sleeping on the sofas.
Compare sohvalla (on the sofa) with sohvilla (on the sofas): the plural has -i- — and here you can also see that the stem vowel a changed to i, which is the subject of the plural stem changes page. For now, notice only that the plural is marked by -i-.
Harmony still applies
The plural -i- is a neutral vowel, so it does not disturb vowel harmony. Back-vowel words keep back endings, front-vowel words keep front endings, exactly as in the singular:
| Word | Plural inessive | Harmony |
|---|---|---|
| talo (house) | taloissa | back → -ssa |
| kauppa (shop) | kaupoissa | back → -ssa |
| kylä (village) | kylissä | front → -ssä |
| metsä (forest) | metsissä | front → -ssä |
So taloissa has the back ending -ssa, but metsissä (in the forests) has the front -ssä — the -i- between them changes nothing about the harmony class of the word. (Kylä and metsä also drop their -ä before the -i-; that stem change is handled on the next page.)
Suomessa on paljon järviä ja niissä metsissä on hiljaista.
Finland has many lakes, and it's quiet in those forests.
Kaupoissa oli tänään paljon tarjouksia.
There were a lot of sales in the shops today.
Where the two markers meet
It helps to see the full split laid out once. A single noun uses -t for exactly one job and -i- for everything else:
| Meaning | Form | Marker |
|---|---|---|
| the cars (subject / total object) | autot | -t |
| in the cars | autoissa | -i- |
| from the cars | autoista | -i- |
| with / at the cars | autoilla | -i- |
| onto / to the cars | autoille | -i- |
English uses one plural, -s, across the whole board: cars, in the cars, from the cars, to the cars. Finnish splits the job — -t at the nominative border, -i- in all the interior country. The commonest beginner error is to let -t leak across that border (*autoteissa, *autotilla); the cure is simply to remember that -t never appears inside a plural once a case ending is attached.
Lapset istuivat autoissa ja odottivat vanhempiaan.
The children sat in the cars and waited for their parents.
Common Mistakes
❌ Asun näissä talotissa.
Incorrect — the oblique plural is not built on -t; use the -i- stem: taloissa.
✅ Asun näissä taloissa.
I live in these houses.
❌ Kirjat ovat hyllylla.
Incorrect — 'on the shelves' needs the plural -i-: hyllyillä (with the front ending, -llä).
✅ Kirjat ovat hyllyillä.
The books are on the shelves.
❌ Kaikki tavarat ovat laatikossa.
Incorrect if you mean several boxes — without the -i- this says 'in the box' (singular); 'in the boxes' is laatikoissa.
✅ Kaikki tavarat ovat laatikoissa.
All the things are in the boxes.
❌ Kävelimme metsassa koko päivän.
Incorrect — for 'in the forests' the plural -i- is missing and so is front harmony: metsissä.
✅ Kävelimme metsissä koko päivän.
We walked in the forests all day.
Key Takeaways
- Every plural case except the nominative/accusative is built on stem + -i- + ending: talo → taloissa, taloista, taloille.
- The -i- is the real plural marker of Finnish — -t covers one case, -i- covers the other twelve.
- Turn a singular oblique into a plural by inserting -i- before the case ending: talossa → taloissa.
- Harmony is unaffected: taloissa (back) versus metsissä (front). The -i- is neutral.
- Never build an oblique plural on -t (*talotissa) — that ending lives only in the nominative.
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Start learning Finnish→Related Topics
- The Plural Marker -t (Nominative)A1 — The nominative plural adds -t to the stem (talo→talot, käsi→kädet). It marks plural subjects and total objects — and no other case uses it.
- Plural Stem Changes: talo → taloi-, poika → poji-B2 — How the plural -i- fuses with the stem vowel: a→o or dropped, ä/e dropped, long vowels shorten, plus gradation that can co-occur (poika→poji-).
- Plural Formation in the Partitive and GenitiveB1 — The two trickiest plural cases: partitive plural (-ja/-jä, -ia/-iä, -ita/-itä) and genitive plural (-jen, -ien, -iden, old -ten), allomorphs sorted out.
- Inessive -ssa/-ssä: 'in'A1 — The inessive -ssa/-ssä means 'inside' (talossa, Helsingissä): location within, time within, and set idioms — and the ending forces the weak grade.
- Plural Stem Errors: talois-, poikas-B2 — Finnish builds its two plurals on two different stems — the -t plural and the -i- plural — and English speakers keep mixing them up. Wrong→right drills.