Learn Hardcore Finnish: Suomessa pääsiäinen on rauhallinen juhlapäivä.

Suomessa is in the inessive case (the “inside-where” case), marked by -ssa / -ssä.
It typically means “in / inside / within” something.

So Suomessa = “in Finland”.
The inessive answers the question missä? (“where?”).

Why is it Suomessa and not just Suomi for “in Finland”?

Suomi is the base form (nominative) meaning “Finland”.
To say “in Finland”, Finnish doesn’t use a separate preposition like “in”; instead it adds a case ending to the noun:

Suomi (Finland)
Suome-ssa → Suomessa = in Finland

So the ending -ssa does the job of the English preposition “in.”

Why is it -ssa and not -ssä in Suomessa?

The choice between -ssa and -ssä follows vowel harmony:

Words with only back vowels (a, o, u) take -ssa.
Words with only front vowels (ä, ö, y) take -ssä.
Mixed or neutral-vowel words follow the main back/front vowels.

Suomi has back vowels u, o, so it takes -ssa → Suomessa.
If the word had front vowels, like pöytä “table”, it would be pöydässä (“on/at the table”).

Why isn’t pääsiäinen capitalized, even though “Easter” is in English?

In Finnish, names of holidays are normally written with a lowercase letter, unless they begin a sentence:

pääsiäinen = easter
joulu = christmas
vappu = may day

English capitalizes many holidays; Finnish usually doesn’t.
So pääsiäinen in the middle of the sentence is correctly lowercase.

Which word is the subject of the sentence, and how is the basic structure arranged?

The subject is pääsiäinen (“Easter”).

The core structure is:

pääsiäinen (subject)
on (verb “is”)
rauhallinen juhlapäivä (predicate: what Easter is)

Suomessa (“in Finland”) is an adverbial of place.

So in English order you could think:
“In Finland, [Easter] [is] [a peaceful holiday].”

What does the verb on do here, and how would you put this sentence in the past tense?

on is the 3rd person singular present tense of olla (“to be”):

hän on = he/she is
pääsiäinen on = Easter is

To make it past tense, use oli:

Suomessa pääsiäinen oli rauhallinen juhlapäivä.
→ “In Finland, Easter was a peaceful holiday.”

Why are rauhallinen and juhlapäivä in this basic form and not something like rauhallista juhlapäivää?

Here, rauhallinen juhlapäivä is a predicate noun phrase: it describes what pääsiäinen is.

In Finnish, with olla (“to be”) and a definite, simple statement of identity/quality, the predicate normally takes the nominative case (the same “dictionary form” as the subject):

Pääsiäinen on rauhallinen juhlapäivä.
→ subject (nominative) + copula + predicate (nominative)

You would use partitive (e.g. rauhallista juhlapäivää) in more special meanings (incomplete, indefinite, or “a sort of” something), not in this straightforward defining sentence.

What does rauhallinen literally mean, and how is it formed?

rauhallinen means “peaceful, calm”. It’s built from:

rauha = peace
-llinen = a common adjective-forming suffix

So literally, rauhallinen ≈ “full of peace / characterized by peace.”

It behaves like a regular adjective and agrees with the noun:

rauhallinen juhlapäivä (singular)
rauhalliset juhlapäivät (plural “peaceful holidays”)

What kind of word is juhlapäivä, and can it be split into parts?

juhlapäivä is a compound noun:

juhla = celebration, feast, festival
päivä = day

Together: juhlapäivä = “holiday / festive day / celebration day.”

In writing, Finnish usually joins such compounds into one word, not two. You don’t write juhla päivä in standard Finnish.

Could you also say “Suomessa pääsiäinen on rauhallista juhlaa”? What would that mean?

Yes, grammatically you can say:

Suomessa pääsiäinen on rauhallista juhlaa.

Here rauhallista juhlaa is in the partitive singular, and it makes the sentence sound:

more descriptive / qualitative than defining,
a bit like “Easter in Finland is a peaceful kind of celebration.”

The original:

Pääsiäinen on rauhallinen juhlapäivä.
→ more definite, classifying: “Easter is (the kind of thing that is) a peaceful holiday.”

Both are correct, but the nominative version is the straightforward way to define what Easter is.

Can the word order be changed, for example to “Pääsiäinen on rauhallinen juhlapäivä Suomessa”? Does that change the meaning?

You can change the word order:

Pääsiäinen on rauhallinen juhlapäivä Suomessa.

This is still correct and means essentially the same thing.

Differences:

Suomessa pääsiäinen on…
→ Slight emphasis on “in Finland” (contrasting with other countries, for example).
Pääsiäinen on rauhallinen juhlapäivä Suomessa.
→ Slightly more neutral; the focus feels more on Easter, with Suomessa just adding where.

Finnish word order is relatively flexible; moving Suomessa changes emphasis, not the basic meaning.

How would you use this sentence as a model to say “In Finland, Christmas is a peaceful holiday”?

Just replace pääsiäinen with joulu (Christmas):

Suomessa joulu on rauhallinen juhlapäivä.
→ “In Finland, Christmas is a peaceful holiday.”

How do you make this sentence negative: “In Finland, Easter is not a peaceful holiday”?

Use the negative verb ei with ole (the negative form of on):

Suomessa pääsiäinen ei ole rauhallinen juhlapäivä.
→ “In Finland, Easter is not a peaceful holiday.”

The structure is:

[place] [subject] ei ole [predicate in nominative].