Learn Hardcore Finnish: Mummo lukee kirjaa yläkerrassa, ja vaari katsoo televisiota alakerrassa. - Grandma reads a book upstairs, and grandpa watches television downstairs.

informal and warm, like English grandma vs the more formal grandmother
common in spoken Finnish and in family contexts
normally not capitalized in the middle of a sentence, because they are common nouns, not names (here they just happen to start the clauses)

So the sentence feels friendly and family-like, not formal or distant.

Why is it lukee kirjaa and not lukee kirjan?

Kirjaa is in the partitive case, while kirjan is in the genitive/accusative.

Mummo lukee kirjaa
→ Grandma is (in the middle of) reading a book; the action is ongoing or uncompleted, like English is reading.
Mummo lukee kirjan
→ Grandma reads / will read the book (to the end); the action is seen as complete, like reads the whole book / will finish the book.

So here kirjaa fits because we’re just describing what she’s doing right now, not whether she finishes the book.

Why is it katsoo televisiota instead of katsoo television?

Again this is the partitive (televisiota) vs genitive/accusative (television).

katsoa televisiota
= to watch TV (in general), an ongoing activity, not a clearly bounded, “finished” event.
katsoa television
is unusual; literally to watch the television (set) as a complete object. It could sound like staring at the physical device, not watching programs. It’s rarely what you want.

So vaari katsoo televisiota = Grandpa is watching TV (watching programs; ongoing action).

Why does Finnish use the simple present (lukee, katsoo) for “is reading / is watching”?

Finnish normally uses the same present tense for both:

Mummo lukee kirjaa
= Grandma reads a book or Grandma is reading a book (context decides).
Vaari katsoo televisiota
= Grandpa watches TV or Grandpa is watching TV.

If you really want to emphasise the ongoing nature, you can say:

Mummo on lukemassa kirjaa.
Vaari on katsomassa televisiota.

But in everyday language, the plain present (lukee, katsoo) is usually enough and very natural.

What does the -ssa ending in yläkerrassa and alakerrassa mean?

The ending -ssa / -ssä is the inessive case, meaning “in / inside”.

yläkerta = upstairs (the upper floor)
→ yläkerrassa = in the upstairs, i.e. upstairs
alakerta = downstairs (the lower floor)
→ alakerrassa = in the downstairs, i.e. downstairs

So:

yläkerrassa = upstairs
alakerrassa = downstairs

literally “in the upper floor / in the lower floor”.

What is the difference between yläkerrassa and ylhäällä, or alakerrassa and alhaalla?

Both pairs can translate as upstairs / downstairs or up there / down there, but there is a nuance:

yläkerrassa / alakerrassa
→ specifically on the upper floor / on the lower floor of a building (more concrete, floor-based).
ylhäällä / alhaalla
→ literally up (there) / down (there), more general vertical location; not tied to “floors”.

In a house, yläkerrassa / alakerrassa are the most natural for “upstairs / downstairs” as in this sentence.

Why is there a comma before ja in ..., ja vaari katsoo...?

In Finnish, you usually put a comma between two independent clauses (two main sentences), even if they are joined by ja.

Here we have:

Mummo lukee kirjaa yläkerrassa
vaari katsoo televisiota alakerrassa

They have different subjects (mummo vs vaari), so they are clearly two separate main clauses. Therefore, you write:

Mummo lukee kirjaa yläkerrassa, ja vaari katsoo televisiota alakerrassa.

If the subject were the same and not repeated, a comma might be omitted, but with two different subjects, the comma is standard.

Is the word order fixed, or could I say Yläkerrassa mummo lukee kirjaa?

Finnish word order is fairly flexible, and you can move elements for emphasis or topic. All of these are possible:

Mummo lukee kirjaa yläkerrassa.
Yläkerrassa mummo lukee kirjaa.
Yläkerrassa lukee mummo kirjaa. (more marked/emphatic)

The neutral, most typical order is:

Subject – Verb – Object – Place
Mummo lukee kirjaa yläkerrassa.

Putting yläkerrassa first (Yläkerrassa mummo lukee kirjaa) emphasizes the location (“Upstairs, grandma is reading a book…”), which is fine if that’s what you want to highlight.

Why do lukee and katsoo end in -ee / -oo?

These are the 3rd person singular present tense forms of the verbs:

lukea (to read) → hän lukee (he/she reads)
katsoa (to watch, to look) → hän katsoo (he/she watches)

Conjugation pattern (present tense):

minä luen / katson – I read / watch
sinä luet / katsot – you read / watch
hän lukee / katsoo – he/she reads / watches
me luemme / katsomme – we read / watch
te luette / katsotte – you (pl.) read / watch
he lukevat / katsovat – they read / watch

So lukee and katsoo are just the regular 3rd person singular forms used with mummo and vaari.

Could I replace mummo and vaari with pronouns like hän?

You can, but you must avoid ambiguity:

After mentioning mummo, you could say:
Mummo lukee kirjaa yläkerrassa. Hän on väsynyt.
(“Grandma is reading a book upstairs. She is tired.”)
In your original compound sentence, if you say:
Mummo lukee kirjaa yläkerrassa, ja hän katsoo televisiota alakerrassa.
hän naturally refers to mummo, so it sounds like Grandma is reading upstairs, and she is watching TV downstairs, which is contradictory.

Because the second clause has a different subject, you must say vaari, not hän, to make it clear.

So the original repetition (mummo … vaari …) is correct and natural here.

Why is it kirjaa and televisiota, not kirja and televisio?

In Finnish, objects often appear in a case form, not in the bare nominative.

kirja (nominative) → kirjaa (partitive)
televisio (nominative) → televisiota (partitive)

You use the partitive here because:

the actions (lukee, katsoo) are ongoing / uncompleted
you are not talking about a single, clearly finished “whole” (like “reads the entire book from start to finish”)

Using bare nominative (kirja, televisio) as a direct object is usually wrong; you almost always need partitive or genitive/accusative instead, depending on meaning.

Are there more colloquial words for televisio in this kind of sentence?

Yes, in everyday speech Finns often say:

telkkari (very common colloquial word for TV)
telkku (even more colloquial / playful)

With the same structure:

Vaari katsoo telkkaria alakerrassa.
Vaari katsoo telkkua alakerrassa.

Televisio is perfectly normal and neutral, but telkkari sounds more informal and spoken, matching the family context of mummo and vaari.