Oikaisuvaatimuksen pitää olla kirjallinen.

The basic form is oikaisuvaatimus.

It is a compound noun:

• oikaisu = correction, rectification
• vaatimus = demand, claim, request

So oikaisuvaatimus is a formal/legal term meaning something like a request for rectification or an appeal for correction.

In the sentence, it appears as oikaisuvaatimuksen, which is not the dictionary form.

Because this sentence uses the Finnish necessity construction with pitää.

A very common pattern is:

jonkun pitää tehdä jotain
= someone must do something

In that pattern, the person or thing that has the obligation often appears in the genitive case, which usually has the ending -n in the singular.

So:

• oikaisuvaatimus = the request for rectification
• oikaisuvaatimuksen = of the request for rectification / the request for rectification as the logical subject of pitää

Even though this does not sound natural if translated word-for-word into English, it is normal Finnish grammar.

Yes, pitää has several meanings in Finnish. Here it means must or has to.

Common meanings of pitää include:

• pitää kädessä = to hold in the hand
• pitää jostakin = to like something
• pitää tehdä = must do

In this sentence, it is clearly the must / has to meaning because it is followed by another verb in the infinitive:

• pitää olla = must be

So Oikaisuvaatimuksen pitää olla kirjallinen means that the request is required to be in written form.

In this kind of necessity construction, pitää normally stays in the 3rd person singular form, regardless of who or what has the obligation.

For example:

• Minun pitää lähteä. = I have to leave.
• Sinun pitää odottaa. = You have to wait.
• Oikaisuvaatimuksen pitää olla kirjallinen. = The request for rectification must be in writing.

So even though English changes the subject normally, Finnish keeps pitää in this fixed form in this structure.

Because pitää needs another verb to say what must happen.

Here the action/state is olla kirjallinen = to be written / to be in writing.

So the structure is:

• oikaisuvaatimuksen = the thing that has the obligation
• pitää = must
• olla = be
• kirjallinen = written / in written form

Literally, the sentence is built like:

the request-for-rectification must be written

In smoother English, this is usually expressed as must be in writing.

Here kirjallinen means in written form or written.

In legal or administrative Finnish, kirjallinen often means that something must be submitted as text, not just said aloud.

So it does not mean specifically:

• handwritten
• beautifully written
• literary

It simply means that the request must exist in writing.

That is why the best English translation is often:

• must be in writing rather than
• must be written

even though both are close.

Because kirjallinen is a predicate adjective after olla.

In Finnish, predicate adjectives are usually in the nominative:

• Talo on suuri. = The house is big.
• Hakemus on valmis. = The application is ready.
• Oikaisuvaatimuksen pitää olla kirjallinen. = The request for rectification must be in writing.

Even though oikaisuvaatimuksen is in the genitive because of the pitää construction, the adjective after olla stays in its normal predicate form: kirjallinen.

In standard written Finnish, the expected form is:

Oikaisuvaatimuksen pitää olla kirjallinen.

That is because the necessity construction with pitää normally takes the logical subject in the genitive.

You may hear less formal spoken Finnish where case marking is reduced or simplified, but in official, careful Finnish, especially in legal or administrative language, oikaisuvaatimuksen is the correct form.

Yes. It sounds clearly formal and fits legal or bureaucratic Finnish.

That comes from both:

• the noun oikaisuvaatimus, which is an official/legal term
• the whole sentence structure, which is typical of instructions and regulations

In everyday speech, people would probably use simpler words and might say something like:

• Sen pitää olla kirjallinen. = It has to be in writing.
• Oikaisupyyntö pitää tehdä kirjallisesti. = The correction request must be made in writing.

But in official documents, the original sentence sounds perfectly natural.

Finnish does not have articles like a and the.

So oikaisuvaatimus or oikaisuvaatimuksen can mean:

• a request for rectification
• the request for rectification

The exact interpretation depends on context.

In official instructions like this, English often uses the because the sentence is talking about a specific type of document in general:

The request for rectification must be in writing.

But Finnish does not need a separate word for that.