Learn Hardcore Finnish: Sunnuntai on rauhallinen päivä.

Yes, in normal full sentences you use on for “is” in the present tense. Unlike in Russian or Arabic, Finnish normally does not drop this verb in standard neutral sentences like this.

Why is there no word for “a” or “the” in the sentence?

Finnish has no articles at all—no direct equivalents of English “a / an” or “the”.

So:

päivä can mean a day or the day depending on context.
rauhallinen päivä can mean a peaceful day or the peaceful day.

In this specific sentence, context leads you to understand it as “Sunday is a peaceful day” (a general description of Sunday as a type of day), but Finnish doesn’t mark that grammatically with separate words.

Why are rauhallinen and päivä both in this form? Are they singular? What case is this?

Yes, both rauhallinen and päivä are:

singular
nominative case

Breakdown:

Sunnuntai – nominative singular (subject)
on – 3rd singular of olla
rauhallinen – nominative singular adjective
päivä – nominative singular noun

In sentences of the type “X is Y” (where Y is a noun phrase describing what X is), Finnish typically puts both the subject and the “Y-part” in the nominative:

Sunnuntai on rauhallinen päivä. – Sunday is a peaceful day.
Helsinki on suuri kaupunki. – Helsinki is a big city.
Koira on uskollinen eläin. – A dog is a loyal animal.

The adjective rauhallinen agrees with päivä in:

number (singular)
case (nominative)

So you see rauhallinen (not rauhallista) and päivä (not päivää).

Why is it rauhallinen päivä and not päivä rauhallinen like in some languages?

In Finnish, the normal order is:

adjective + noun

So:

rauhallinen päivä – peaceful day
iso talo – big house
vanha auto – old car

Putting the adjective after the noun (päivä rauhallinen) is not normal Finnish and would generally be wrong in this kind of sentence.

You can, however, put the whole phrase before or after the verb:

Sunnuntai on rauhallinen päivä.
Rauhallinen päivä on sunnuntai. – Grammatically OK, but now it emphasizes “It is Sunday that is the peaceful day.”

The adjective’s position relative to the noun usually doesn’t change: the adjective comes first.

Why isn’t it SunnuntaI with a long vowel at the end, like Sunnuntaii?

The word sunnuntai is pronounced with:

stress on the first syllable: SUN-nun-tai
the last syllable -tai has the diphthong ai, not a long vowel

So:

tai = one syllable, /taɪ/ (like English tie)
No double i, so not sunnuntaii

Finnish long vowels are written with double vowels (aa, ee, ii, oo, uu, yy, ää, öö), so if there were a long i, you’d see ii in spelling. Because you don’t, you know it’s a normal-length /i/ as part of a diphthong ai.

Could the sentence also be Sunnuntai on rauhallinen without päivä?

Yes, you can say:

Sunnuntai on rauhallinen.

This would usually be understood as:

“Sunday is peaceful.” / “Sunday is calm.”

Here rauhallinen works as a predicative adjective describing Sunnuntai directly, without an extra noun. It’s like English “Sunday is quiet.”

So:

Sunnuntai on rauhallinen päivä. – Sunday is a peaceful day.
Sunnuntai on rauhallinen. – Sunday is peaceful.

Both are grammatically correct; the version with päivä just makes explicit that you are talking about Sunday as a day.

Why is it päivä and not päivää? When would I use päivää instead?

Päivä (without the extra ä) is nominative singular.
Päivää (with the extra ä) is partitive singular.

In a sentence like “X is Y (a kind of thing)”, Finnish normally uses the nominative for Y:

Sunnuntai on rauhallinen päivä. – complete classification: Sunday is a peaceful day (as a type of day).

You would use päivää (partitive) in, for example:

Object meanings:
- Näen päivän. – I see the day (whole day; nominative).
- Näen päivää. – I see (some) day / daylight (partial / unbounded; partitive).
Certain predicative structures expressing incompleteness or ongoingness, or with certain verbs, but in a simple “X is a Y” definition like this, nominative (päivä) is the standard choice.

So in this sentence, using päivää would be unidiomatic and suggest a different structure or meaning; päivä is correct.

How would I say “Sundays are peaceful days” instead?

To make both subject and predicate plural, you change:

Sunnuntai → Sunnuntait (nominative plural)
on → ovat (3rd person plural of olla)
rauhallinen → rauhallisia (adjective in partitive plural, agreeing with the noun)
päivä → päiviä (partitive plural)

One natural option:

Sunnuntait ovat rauhallisia päiviä.
– Sundays are peaceful days.

You could also express a habitual idea without pluralizing Sunday:

Sunnuntaisin on rauhallista. – On Sundays, it is peaceful.
(Here sunnuntaisin is an adverbial form meaning “on Sundays.”)

What’s the difference between Sunnuntai on rauhallinen päivä and Sunnuntaina on rauhallinen päivä?

They mean different things:

Sunnuntai on rauhallinen päivä.
– Sunday is a peaceful day.
This is a general statement describing Sunday as a kind of day.
Sunnuntaina on rauhallinen päivä.
– Literally: “On Sunday there is a peaceful day.”
- sunnuntaina is the essive form (often used for “on [a certain day]”).
- This is more like saying “On Sunday there will be / there is a peaceful day (some peaceful day or event)”, and is not a natural way to make the generic “Sunday is a peaceful day” statement.

More idiomatic uses of sunnuntaina:

Sunnuntaina on juhla. – There is a celebration on Sunday.
Sunnuntaina on hyvä levätä. – On Sunday it is good to rest.

For describing Sunday as a type of day, the original sentence with nominative Sunnuntai is the natural one.

Can I leave out on, like Sunnuntai rauhallinen päivä?

In normal, standard sentences, you cannot leave out on here. You need the verb:

Sunnuntai on rauhallinen päivä. – correct
Sunnuntai rauhallinen päivä. – incorrect in normal prose

There are two notable exceptions:

Headlines / titles often drop on:
- Sunnuntai – rauhallinen päivä (in a heading or poster).
Colloquial speech may sometimes omit on in very specific patterns, but for a learner and in standard language, you should always include on in this kind of sentence.

How do you pronounce rauhallinen and why is there a double l?

Rauhallinen is pronounced roughly like:

RAU-hal-li-nen

Details:

stress: always on the first syllable: RAU-
rau: a diphthong au with r before it, like “row” but with trilled or tapped r.
ll: a long consonant; you hold the l slightly longer than in English. It splits the syllables: hal-li.
-nen: pronounced -nen, almost like “nen” in “linen”.

In Finnish, double consonants (kk, tt, pp, ll, etc.) are genuinely longer than single ones and can change meaning:

tuli – fire
tulli – customs (border control)

So the double l in rauhallinen must be pronounced longer than a single l.