Cases in the Plural | Finnish Grammar

Finnish has two completely different ways of building a plural, and the split falls exactly on one line: the nominative and accusative plural use the marker -t (talot "houses"), but every other case builds its plural on the -i- plural stem, onto which the ordinary case ending is then attached (taloissa "in the houses"). This is the single most important fact about the Finnish plural, because it means the -t you learn first is a false friend — it appears in only two of the fifteen cases. For "in the houses" you do not add anything to talot; you rebuild the word on a different stem.

Two plural markers, two different jobs

Marker	Where it appears	Example
-t	Nominative & accusative plural only	talot (houses)
-i-	Every other case (the oblique plural stem)	taloi- → taloissa (in the houses)

The -t form names the plural as a subject or as a total object; that is the extent of its territory. The moment you want to say in, into, out of, on, with, as the houses, the -t disappears and the -i- stem takes over.

Talot ovat kalliita tällä alueella.

Houses are expensive in this area. (nominative plural -t)

Näissä taloissa asuu paljon opiskelijoita.

A lot of students live in these houses. (inessive plural, -i- stem)

Muutimme yhdestä vanhasta talosta toiseen.

We moved from one old house to another.

The contrast talot (nominative) versus taloi-ssa (inessive) is the pattern to burn in: there is no -t in the oblique plural. Taloissa has an -i-, not a -t-.

Running one noun through the cases

The cleanest way to see the system is to line the singular and plural up side by side. Notice that outside the nominative every plural form contains -i- right where the singular has nothing.

Case	Singular	Plural	Meaning (pl.)
Nominative	talo	talot	houses
Genitive	talon	talojen	of the houses
Partitive	taloa	taloja	houses (partial)
Inessive	talossa	taloissa	in the houses
Elative	talosta	taloista	out of the houses
Illative	taloon	taloihin	into the houses
Adessive	talolla	taloilla	on/at the houses
Ablative	talolta	taloilta	off the houses
Allative	talolle	taloille	onto the houses
Essive	talona	taloina	as houses
Translative	taloksi	taloiksi	into houses

Kaupungin taloista puolet on tyhjillään talvella.

Half of the town's houses stand empty in winter.

Muutimme kolmesta pienestä asunnosta yhteen isoon.

We moved from three small flats into one big one.

The genitive and partitive plurals (talojen, taloja) look a little different because they take -j- between the stem and the ending — those two cases have their own special formation and are handled on the plural partitive and genitive page. Every other plural is a plain "-i- stem plus case ending", exactly as the table shows.

When the -i- fuses with the stem vowel

The -i- does not always sit visibly beside the stem vowel; the two often merge, and this is where the real work of the plural lives. A few reliable patterns:

A stem ending in -o, -ö, -u, -y simply keeps its vowel and adds -i-: talo → taloi- (taloissa), kylpy → kylvyi- (kylvyissä).
A two-syllable -a stem whose first vowel is a, e, or i changes its final -a to -o: kirja → kirjoi- (kirjoissa "in the books"), kissa → kissoi- (kissoissa).
Other stems drop or alter the final vowel entirely: poika → poji- (pojissa "in the boys"), käsi → käsi- built on käs- (käsissä "in the hands", käsillä "with/on the hands").

Vastaukset ovat kirjoissa, jos vain viitsit etsiä.

The answers are in the books, if you just bother to look.

Kannoin kaikki ostokset käsissäni yhtä aikaa.

I carried all the shopping in my hands at once.

Pojilla oli lumipallot valmiina jo pihalla.

The boys already had snowballs ready in the yard.

Notice käsi especially: its nominative plural is kädet (built on the weak-grade stem käde-), but its oblique plural is käs-i- — käsissä, käsille, käsiin. The same word uses two different stems for its two kinds of plural, which is precisely why "the hands are cold" (kädet ovat kylmät) and "in my hands" (käsissäni) look so unlike each other. The full inventory of these vowel changes is laid out on the plural stem changes and plural -i- stem pages; the point to carry away here is that the case ending is the easy part — it is the same ending as in the singular — while the -i- stem is where the irregularity concentrates.

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Build an oblique plural in two moves, in this order: (1) form the -i- plural stem (this is the hard, word-specific step), then (2) bolt on the same case ending you already know from the singular. Talo → stem taloi- → add inessive -ssa → taloissa. Never start from the nominative plural talot.

Adjectives agree in the plural too

When a plural noun sits in a case, its adjectives take the same case and the same plural stem — Finnish agreement is total. So "in the big houses" repeats the -i- stem and the inessive ending on both words:

Vanhoissa taloissa on korkeat katot ja isot ikkunat.

Old houses have high ceilings and big windows.

Puhuin monille eri ihmisille samasta asiasta.

I talked to many different people about the same thing.

Vanhoissa taloissa, monille ihmisille — both the adjective and the noun carry the plural stem and the case. This agreement is the subject of the case and adjective page; here just note that once you know the noun's plural case form, the adjective simply copies it.

Common Mistakes

❌ Asun näissä talotissa.

Incorrect — the oblique plural is built on the -i- stem, not on the -t plural: taloissa.

✅ Asun näissä taloissa.

I live in these houses.

❌ Kirjat ovat laukussa; etsi vastaus kirjatista.

Incorrect — 'from the books' uses the -i- stem: kirjoista.

✅ Etsi vastaus kirjoista.

Look for the answer in the books.

❌ Kannoin kassit kädeissäni.

Incorrect — the oblique plural of käsi is built on the stem käs-i- (käsissäni), not on the nominative-plural stem käde- (kädet).

✅ Kannoin kassit käsissäni.

I carried the bags in my hands.

❌ Menen taloihin — ei, tarkoitan talotihin.

Incorrect — the illative plural is taloihin; there is no -t- in it.

✅ Menemme naapureiden taloihin vuorotellen.

We go into the neighbours' houses in turn.

Key Takeaways

The plural marker -t appears only in the nominative and accusative (talot); every other case builds on the -i- plural stem (taloissa).
Form an oblique plural in two steps: build the -i- stem first, then add the normal case ending — taloi- + -ssa = taloissa.
The genitive and partitive plurals are special (talojen, taloja) — see plural partitive and genitive.
The -i- often fuses with the stem vowel: kirja → kirjoissa, poika → pojissa, käsi → käsissä (with nominative plural kädet on a different stem).
Adjectives agree fully: vanhoissa taloissa, monille ihmisille.

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