Kirjallinen oikaisuvaatimus sisältää perusteen ja perustelun.

Because Finnish uses compound nouns very freely, and they are usually written as a single word.

Here, oikaisuvaatimus is made from:

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

So oikaisuvaatimus is a fixed legal/administrative term meaning something like request for rectification or claim for correction.

English often writes these as separate words, but Finnish usually joins them into one compound.

Here kirjallinen means written or in writing.

Even though kirjallinen can sometimes mean literary in other contexts, that is not the meaning here. In legal or administrative language, kirjallinen oikaisuvaatimus means a rectification request that is made in written form.

It is in the nominative singular because it agrees with the noun oikaisuvaatimus, which is also nominative singular.

So:

• kirjallinen = written
• oikaisuvaatimus = rectification request

Together they form the subject of the sentence:

• Kirjallinen oikaisuvaatimus = a written rectification request

In Finnish, adjectives usually match the noun they describe in number and case.

Finnish does not have articles like English a, an, or the.

So kirjallinen oikaisuvaatimus can mean:

• a written rectification request
• the written rectification request

Which one sounds best in English depends on context. Finnish leaves that distinction to the situation, context, or style.

Because they are singular total objects in this sentence.

The verb sisältää means to contain / include, and here it is talking about complete items that the request includes. In Finnish, a complete singular object often appears in a form that looks like the genitive singular:

• peruste → perusteen
• perustelu → perustelun

So:

• sisältää perusteen = includes a ground/basis
• sisältää perustelun = includes a justification/explanation

This is very normal Finnish object marking.

This is a very common learner question.

Short answer: they are objects, but in the singular they often have a form that looks exactly like the genitive.

So:

• by form, they look genitive
• by function, they are the objects of the verb

Many grammar explanations say that the Finnish total object in the singular is identical in form to the genitive. So if you were wondering why an object does not look like an English-style direct object, that is the reason.

A useful contrast:

• affirmative: sisältää perusteen
• negative: ei sisällä perustetta

In the negative sentence, Finnish uses the partitive instead.

They are related, but not the same.

• peruste = a basis, ground, reason, legal ground
• perustelu = a justification, explanation, argumentation

A simple way to see the difference:

• peruste answers: On what basis?
• perustelu answers: How do you explain or support it?

In legal or formal writing, this distinction is useful. A person may give the ground for the claim and also the justification/explanation for it.

The singular here can be understood generically: the written request must include this kind of information.

So even if, in real life, a document may contain several grounds or several arguments, Finnish can still use the singular in a general rule-like statement.

A plural version would also be possible in some contexts:

• perusteet ja perustelut = grounds and justifications

But the sentence as written presents the required content in a more general, category-like way.

No, this is a very normal Finnish word order.

The sentence follows the basic pattern:

• subject: Kirjallinen oikaisuvaatimus
• verb: sisältää
• object(s): perusteen ja perustelun

So it is a straightforward Subject–Verb–Object sentence.

Finnish word order can be changed for emphasis, but this version is neutral and very natural, especially in formal or legal language.