Learn Hardcore Finnish: Tuuli tekee aallot korkeiksi merellä. - The wind makes the waves tall on the sea.

It’s the translative case, which expresses a change of state or a resulting role. With verbs like tehdä (to make), tulla (to become), or nimetä (to name), you put the new state in the translative. Example: Hän maalasi seinät valkoisiksi (He painted the walls white).

Why is it korkeiksi (plural) and not korkeaksi (singular)?

Because the predicative adjective agrees in number with the object. The object is plural (aallot), so the result state is plural too: korkeiksi. If the object were singular (e.g., aallon or aalto), you’d use korkeaksi.

Why is the object aallot and not aaltoja?

Aallot is a total object (a specific, complete set) because the wind makes the waves (as a whole set) high. Aaltoja (partitive) would suggest an indefinite or incomplete quantity: Tuuli tekee aaltoja means the wind produces/creates waves. Compare: Tuuli tekee korkeita aaltoja = it creates high waves (not “makes the waves high”).

Is aallot nominative or accusative here?

Formally it’s nominative plural, but functionally it’s a total object. Finnish marks plural total objects with the nominative plural form (aallot) in affirmative clauses. Partitive (aaltoja) would mark an incomplete/indefinite object.

What’s going on with merellä instead of meressä or merelle?

merellä (adessive, -llä) = on/at sea, out at sea (surface/open area; the idiomatic choice here).
meressä (inessive, -ssa) = in the sea, inside the water.
merelle (allative, -lle) = to the sea, out to sea (movement).
So merellä is the natural way to say “at sea.”

Can I change the word order?

Yes. Finnish allows flexible order for emphasis.

Merellä tuuli tekee aallot korkeiksi highlights the location.
Tuuli tekee merellä aallot korkeiksi emphasizes where the making happens.
Aallot tuuli tekee merellä korkeiksi focuses on the waves.
The core meaning stays; the focus shifts.

Could I drop merellä?

Yes: Tuuli tekee aallot korkeiksi still means the wind makes the waves high, just without specifying the location. Adding merellä localizes it to “at sea.”

How is each word formed?

Tuuli: nominative singular of “wind.”
tekee: 3rd person singular present of tehdä (to do/make).
aallot: nominative plural of aalto (wave).
korkeiksi: translative plural of korkea (high/tall).
merellä: adessive singular of meri (sea).

Why does aalto become aallot with double L?

It’s due to consonant changes in the stem: aalto inflects with a stem aallo- before certain endings, giving aallot (nom. pl.) and aallon (gen. sg.). You hear both the long vowel (aa) and long consonant (ll).

Why does korkea become korkeiksi and not something like korkeaiksi?

The adjective’s stem is korke-. When you add plural -i- and translative -ksi, you get korke-i-ksi → korkeiksi. The ea in korkea reduces to e in the stem.

Can I say korkeina instead of korkeiksi?

No. Korkeina is essive plural (“as high”) and describes a state rather than a result of change. After tehdä (“make”), you need the translative to show the resulting state: korkeiksi.

Does tekee here mean “does” or “makes”?

Here it means “makes.” The pattern tehdä + object + adjective-ksi means “to make [object] [adjective].” Example: Se teki minut iloiseksi (It made me happy).

How would I say “higher,” not just “high”?

Use the comparative in the translative plural: korkeammiksi.
Example: Tuuli tekee aallot korkeammiksi merellä (The wind makes the waves higher at sea).

Are there natural alternatives to say the same idea?

Yes:

Tuuli nostaa aallot korkeiksi (The wind raises the waves to be high).
Tuuli saa aallot korkeiksi (The wind gets/causes the waves to be high).
Or describe the state: Kun tuulee, aallot ovat korkeita merellä (When it’s windy, the waves are high at sea).