The Superlative -in: 'most' | Finnish Grammar

Just as the comparative packs "more" into a suffix, the superlative packs "most" into one too. To say "biggest, oldest, most beautiful," Finnish adds -in to the adjective's stem: iso → isoin, vanha → vanhin, kaunis → kaunein. There is no separate most — the peak of the scale lives inside the word. The only real work is knowing what happens to the stem's final vowel when the -i- of -in lands on it.

The basic pattern: stem + -in

The superlative marker is -in in the nominative. Attach it to the adjective stem and adjust the final vowel:

Adjective	Superlative	Meaning
iso	isoin	biggest
vanha	vanhin	oldest
nuori	nuorin	youngest
suuri	suurin	biggest, greatest
kaunis	kaunein	most beautiful

Tämä on kylän vanhin talo.

This is the oldest house in the village.

Nuorin lapsista on vasta kolmevuotias.

The youngest of the children is only three years old.

Se oli elämäni kaunein hetki.

It was the most beautiful moment of my life.

What happens to the stem vowel before -in

The -i- of the superlative behaves like the plural -i-: it forces the stem's final vowel to change. Four patterns cover almost everything:

Stem ends in…	Change before -in	Example
-o, -ö, -u, -y	stays, joins the i as a diphthong	iso → isoin
-a, -ä	drops	vanha → vanhin, nopea → nopein
-e	drops	suuri (suure-) → suurin
long -ii	becomes -ei-	kaunis (kaunii-) → kaunein

Kuka on luokan nopein juoksija?

Who is the fastest runner in the class? (nopea → nopein)

Tammikuu on vuoden kylmin kuukausi.

January is the coldest month of the year. (kylmä → kylmin)

Everest on maailman korkein vuori.

Everest is the highest mountain in the world. (korkea → korkein)

The one that surprises people is kaunis → kaunein: the long -ii- of the stem kaunii- collapses into -ei-. The same happens to kallis → kallein ("most expensive"). These are not exceptions so much as the regular fate of a long -ii- meeting the superlative -i-.

Se ei suinkaan ollut kaupungin kallein ravintola.

It certainly wasn't the most expensive restaurant in town. (kallis → kallein)

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Notice how the superlative vanhin drops the -a while the comparative vanhempi turns it into -e-. That is the cleanest way to keep the two apart: the comparative -mpi tends to keep a vowel before it (often shifting a/ä → e), whereas the superlative -ineats the final a/ä/e outright.

The superlative declines too

Like the comparative, the superlative is a full adjective and inflects in every case, agreeing with its noun. When it inflects, the -in changes to -imma-/-immä-: isoin → isoimman (genitive), isoimmassa (inessive), isoimmat (plural). The one form that keeps the -in is the partitive singular: isoin → isointa.

Asumme kaupungin vanhimmassa talossa.

We live in the oldest house in the city. (inessive isoimman-type: vanhimmassa)

Annoin tehtävän luokan nopeimmalle oppilaalle.

I gave the task to the fastest pupil in the class. (allative nopeimmalle)

The full paradigm — the -in → -imma- alternation and the partitive -inta/-intä — has its own page: superlative stem changes. For now, register that isoin becomes isoimma- the moment a case ending arrives.

"The …-est of": genitive, elative, or kaikista

Finnish expresses "the biggest of the group" in a few ways. Most compactly, the group goes into the genitive or elative before the superlative:

Hän on perheen pisin.

She is the tallest in the family. (genitive: perheen)

Kumpi näistä on parempi — ja mikä kaikista paras?

Which of these two is better — and which is the best of all?

The word kaikista ("of all") or the intensifier kaikkein often stands before the superlative to mean "the very -est":

Tämä reitti on kaikista lyhin.

This route is the shortest of all.

The one you must memorise: hyvä → paras

Exactly as in the comparative, hyvä ("good") is suppletive in the superlative. Its "most" form is not *hyväin but paras ("best"), from an entirely different root:

Tämä on paras päätös, jonka olen tehnyt.

This is the best decision I've ever made.

Hän on paras ystäväni.

She is my best friend.

Paras inflects on the stem parhaa-: parhaan (genitive), parasta (partitive), parhaassa (inessive), parhaat (plural). A few other adjectives have irregular superlatives — pitkä → pisin ("longest"), lyhyt → lyhin ("shortest") — collected on the irregular comparison page. But hyvä → paras is the one to know cold.

Tämä on maailman pisin joki.

This is the world's longest river. (pitkä → pisin)

Common Mistakes

❌ Tämä on eniten iso talo kylässä.

Incorrect — Finnish uses the suffix -in, not a separate 'most' word: isoin.

✅ Tämä on kylän isoin talo.

This is the biggest house in the village.

❌ Se oli elämäni kauniiin hetki.

Incorrect — the long -ii- collapses to -ei- before the superlative: kaunein, not *kauniiin.

✅ Se oli elämäni kaunein hetki.

It was the most beautiful moment of my life.

❌ Hän on minun hyväin ystäväni.

Incorrect — hyvä is suppletive: the superlative is paras.

✅ Hän on minun paras ystäväni.

She is my best friend.

❌ Asumme kaupungin vanhinssa talossa.

Incorrect — the superlative gradates to -imma- in the oblique cases: vanhimmassa.

✅ Asumme kaupungin vanhimmassa talossa.

We live in the oldest house in the city.

Key Takeaways

The superlative is a suffix, -in, on the adjective stem: iso → isoin, kaunis → kaunein — never a separate most word.
The stem's final vowel adjusts before -i-: -o/-u/-y/-ö joins it (isoin), -a/-ä/-e drops (vanhin, suurin), long -ii- becomes -ei- (kaunein).
The superlative declines (-in → -imma-/-immä-), keeping -in only in the partitive singular (isointa); full paradigm on superlative stem changes.
"The -est of" uses the genitive/elative or kaikista: perheen pisin, kaikista paras.
Hyvä → paras is suppletive — memorise it.

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