Learn Hardcore Finnish: Tämä kerrostalo on korkea ja hiljainen. - This apartment building is tall and quiet.

Context tells you whether it’s more like a or the in English. In this sentence, Tämä kerrostalo clearly means this (particular) apartment building, so it feels like the in English, but Finnish doesn’t add anything extra to mark that.

What does kerrostalo literally mean, and why is it one word?

Kerrostalo is a compound noun:

kerros = floor, storey
talo = house, building

So kerrostalo is literally a multi-storey house/building, i.e. an apartment building / block of flats.

Finnish very often combines nouns into a single compound word instead of keeping them separate. So where English has apartment building (two words), Finnish has kerrostalo (one word).

Why is it Tämä kerrostalo and not Tuo kerrostalo or Se kerrostalo?

All three are demonstratives, but they feel different:

tämä kerrostalo = this apartment building (physically close to the speaker, or psychologically very “here”)
tuo kerrostalo = that apartment building (a bit further away, or mentally more “there”)
se kerrostalo = literally that apartment building, but often used more like a neutral the apartment building when the listener already knows which one is meant

So Tämä kerrostalo on korkea ja hiljainen is specifically This apartment building (right here / we’re looking at it) is tall and quiet.

What is the function of on in this sentence?

On is the third‑person singular form of the verb olla (to be).

olla = to be
hän on = he/she is
se on = it is
Tämä kerrostalo on = This apartment building is

In Finnish, you don’t need to say se (it) here, because Tämä kerrostalo is already the subject. So on simply links the subject Tämä kerrostalo with the adjectives korkea ja hiljainen (tall and quiet), just like is in English.

Why are the adjectives korkea and hiljainen placed after on and not before the noun like in English?

In this sentence, korkea and hiljainen are predicative adjectives: they describe the subject after a form of the verb olla (to be).

English:

This apartment building is tall and quiet. (adjectives after is)

Finnish:

Tämä kerrostalo on korkea ja hiljainen.

So here the pattern is very similar to English:
subject – olla (to be) – adjective(s)

If the adjectives were directly in front of the noun, you would get a slightly different structure and meaning:

korkea kerrostalo = a tall apartment building (adjective directly modifies the noun)
hiljainen kerrostalo = a quiet apartment building

Compare:

Tämä on korkea kerrostalo. = This is a tall apartment building.
Tämä kerrostalo on korkea. = This apartment building is tall.

Both are correct, but they focus slightly differently (what this is vs. what this apartment building is like).

Why do the adjectives not have a plural ending like -t? Why korkea, not korkeat?

Because the subject Tämä kerrostalo is singular. In Finnish, predicative adjectives agree with the subject in number (singular/plural) and usually in case.

singular: Tämä kerrostalo on korkea ja hiljainen.
- kerrostalo (singular) → korkea, hiljainen (singular)
plural: Nämä kerrostalot ovat korkeat ja hiljaiset.
- kerrostalot (plural) → korkeat, hiljaiset (plural with -t)

So you only see -t on the adjectives when the subject is plural.

Which case is kerrostalo in here, and do the adjectives agree in case?

Kerrostalo is in the nominative singular, the basic dictionary form (no ending).

In this structure:

Tämä kerrostalo (subject) → nominative
korkea, hiljainen (predicative adjectives) → also nominative

Yes, predicative adjectives generally agree with the subject in case and number, so all three are nominative singular here:

kerrostalo
korkea
hiljainen

How would I say “This apartment building is not tall or quiet” in Finnish?

You would use the negative verb ei and the basic form ole of olla:

Tämä kerrostalo ei ole korkea eikä hiljainen.

Breakdown:

ei ole = is not
eikä = and not / nor (combination of ja
- ei)

So literally: This apartment building is not tall and-not quiet.

How would I say “These apartment buildings are tall and quiet”?

You need the plural demonstrative and plural noun, and the plural form of olla:

Nämä kerrostalot ovat korkeita ja hiljaisia.

Here there are two possible patterns:

Nämä kerrostalot ovat korkeat ja hiljaiset.
- adjectives in nominative plural (korkeat, hiljaiset)
- describes all of them as a definite set
Nämä kerrostalot ovat korkeita ja hiljaisia.
- adjectives in partitive plural (korkeita, hiljaisia)
- more like describing them as examples of tall, quiet buildings among others

Both are grammatically correct; the partitive plural is very common in this kind of descriptive sentence.

What does hiljainen exactly mean, and are there similar words I might confuse it with?

Hiljainen primarily means quiet or silent:

hiljainen kerrostalo = a quiet apartment building
hiljainen huone = a quiet room

Related or possibly confusing words:

hiljaa = quietly, in a low voice (adverb)
rauhallinen = calm, peaceful (more about atmosphere or situation)
tyyni = calm, often used about weather or water (calm sea, calm wind)

So hiljainen is the default word when you mean low noise level: not much sound coming from the building or inside it.

Why is it ja hiljainen and not something like sekä hiljainen?

Both ja and sekä mean and, but:

ja is the ordinary, neutral and used in everyday speech.
sekä is also and, but sounds a bit more formal or written, often used in lists.

In a simple descriptive sentence like this, ja is the most natural choice:

Tämä kerrostalo on korkea ja hiljainen.

You could say sekä instead, and it would not be wrong, but it would sound more formal or stylistic:

Tämä kerrostalo on korkea sekä hiljainen. (more like written style)

How do I pronounce kerrostalo and hiljainen correctly?

Key points:

kerrostalo

Stress is always on the first syllable: KER-rostalo
Double rr means a longer r sound; hold it slightly: ker-rrr-os
Each vowel is pronounced clearly; nothing is reduced like in English.

hiljainen

Stress on first syllable: HIL-jai-nen
lj is pronounced smoothly, roughly like l followed by y in yes: hil-ya-nen
ai is a diphthong like the eye in English eye.

Rough approximations:

kerrostalo ≈ KER-ross-tah-loh
hiljainen ≈ HIL-yai-nen (with nen as in pen, but shorter)

Can I drop Tämä and just say Kerrostalo on korkea ja hiljainen?

Yes, grammatically you can, but the meaning changes slightly:

Tämä kerrostalo on korkea ja hiljainen.
- this apartment building (a specific one, pointed out)
Kerrostalo on korkea ja hiljainen.
- The apartment building is tall and quiet (one that is already known from context)
- Could also sound a bit generic: An apartment building is tall and quiet (less natural in English, but possible in Finnish in the right context)

So dropping Tämä removes the explicit this and makes the reference depend more on context.