Learn Hardcore Finnish: Torstai-iltana katsomme elokuvaa kotona yhdessä. - On Thursday evening we watch a movie together at home.

In Finnish, many combinations like this are written as one “word” (a compound). When the first part ends in the same vowel the second part begins with, a hyphen is usually added to keep it easy to read:

torstai-ilta (not torstai ilta as two separate words)
without the hyphen it would be torstaiilta, which looks odd and is harder to read at a glance.

So:

Correct: torstai-ilta, in the sentence torstai-iltana
Not correct as two separate words: torstai ilta

What does the -na ending in iltana mean, and how does it relate to the idea “on Thursday evening”?

The ending -na / -nä is the essive case in Finnish.

The bare noun:

ilta = evening
The essive form:
iltana = “as (an) evening”, “in the role of an evening” → used idiomatically for “in the evening / on (a) … evening”

In torstai-ilta → torstai-iltana:

torstai-ilta = Thursday evening (as a noun)
torstai-iltana = on Thursday evening (time when something happens)

Finnish often uses the essive for times, instead of a preposition like on:

maanantaina = on Monday
keväänä = in (the) spring (in some styles/contexts)
jouluaattona = on Christmas Eve

So Torstai-iltana katsomme… literally has “Thursday evening-ESS” and that -na plays the role of English “on (Thursday evening)”.

Could I also say Torstaina illalla instead of Torstai-iltana? Is there any difference?

Yes, you can, and both are natural:

Torstai-iltana katsomme elokuvaa…
Torstaina illalla katsomme elokuvaa…

Both mean roughly “On Thursday evening we (will) watch a movie…”.

Nuance:

torstai-iltana treats “Thursday evening” as one named time slot (like a single unit: “Thursday evening”).
torstaina illalla literally is “on Thursday, in the evening” – it mentions the day and then the time of day separately.

In everyday speech the difference is very small, and they are usually interchangeable. Use whichever feels simpler; you will hear both.

What tense is katsomme? How can the same form mean “we watch” and “we will watch”?

Katsomme is the present tense indicative, 1st person plural of katsoa (“to watch, to look at”).

Finnish has only one simple “present” form, and it often covers:

we watch (habitual)
we are watching (right now)
we will watch (future)

So Torstai-iltana katsomme elokuvaa… can be translated according to context as:

“On Thursday evening we watch a movie…”
“On Thursday evening we’re going to watch a movie…”

If you really want to stress futurity, you can add other words:

Torstai-iltana aiomme katsoa elokuvaa.
“On Thursday evening we are going to watch a movie.”

Why is there no me (“we”) before katsomme? Is it optional?

In Finnish, the person and number of the subject are shown by the ending on the verb, so the subject pronoun is usually optional.

Conjugation of katsoa in the present:

minä katson – I watch
sinä katsot – you watch
hän katsoo – he/she watches
me katsomme – we watch
te katsotte – you (pl.) watch
he katsovat – they watch

The ending -mme in katsomme already tells you “we”, so you can leave me out:

Me katsomme elokuvaa.
Katsomme elokuvaa.

Both are correct. Me is used mainly for emphasis or contrast:

Me katsomme elokuvaa, mutta he lukevat kirjaa.
We are watching a movie, but they are reading a book.

Why is elokuvaa in the partitive case instead of just elokuva?

Elokuvaa is the partitive singular of elokuva (“movie, film”).

Bare noun:

elokuva = movie (nominative)

Partitive:

elokuvaa = some movie / movie (as an ongoing object, not seen as a whole unit)

In this sentence, the verb katsoa (“to watch”) very often takes a partitive object, especially when the action is seen as ongoing or unbounded:

katsoa elokuvaa – watch (some) movie / be in the process of watching a movie
katsoa televisiota – watch TV
kuunnella musiikkia – listen to music

Using the partitive here suggests we focus on the activity of watching, not on the movie as a completed whole unit. That’s why elokuvaa is more natural than plain elokuva in this context.

What’s the difference between katsomme elokuvaa and katsomme elokuvan?

The difference is mainly about aspect / completeness of the action.

katsomme elokuvaa (partitive object)
- Focus on the activity, not on finishing it.
- Translations:
  - “We are watching a movie.”
  - “We watch a movie.” / “We’ll be watching a movie.”
- Doesn’t say whether you finish the whole movie or not; it’s neutral about completion.
katsomme elokuvan (total object – here, genitive singular)
- Emphasizes that you watch the whole movie, from start to finish.
- Typical translation:
  - “We (will) watch the movie (all the way through).”
- In the past tense, the contrast is very clear:
  - Katsoimme elokuvaa. – We were watching a movie (activity, maybe not finished).
  - Katsoimme elokuvan. – We watched the (whole) movie (finished it).

In your sentence about Thursday evening, the neutral, natural choice is katsomme elokuvaa.

Finnish has no words like “a” or “the” here. How do you know whether elokuvaa means “a movie” or “the movie”?

Finnish has no articles like English a / an / the.

The word elokuvaa by itself is neutral: it can correspond to either “a movie” or “the movie”, depending on context.

If you are just stating a general plan and haven’t mentioned any specific film:
- Torstai-iltana katsomme elokuvaa kotona yhdessä.
  → usually translated: “On Thursday evening we (will) watch a movie at home together.”
If the movie is already known from context, it can mean “the movie”:
- (We’ve been talking about a particular film.)
  Torstai-iltana katsomme elokuvaa kotona yhdessä.
  → “On Thursday evening we’ll watch the movie at home together.”

To make “the movie” very explicit, Finnish often uses demonstratives:

katsomme sen elokuvan – we (will) watch that movie / the movie
katsomme sitä elokuvaa – we are watching that movie (in progress)

So definiteness is expressed via context, word order, and words like se / tämä, not with articles.

What exactly does kotona mean, and how is it different from kotiin and kotoa?

All three relate to koti (“home”), but they express different directions:

kotiin – to home, movement towards home
- Mennään kotiin. – Let’s go home.
kotona – at home, static location, no movement
- Olemme kotona. – We are at home.
- In your sentence: katsomme elokuvaa kotona – we watch a movie at home.
kotoa – from home, movement away from home
- Lähden kotoa kello kahdeksan. – I leave home at eight o’clock.

So kotona is used here because the action of watching the movie takes place at home; there is no going or coming implied.

These forms (kotiin, kotona, kotoa) are a bit irregular compared to many other nouns, so they are usually learned as a fixed set.

Is there any rule about where yhdessä (“together”) should go in the sentence?

Yhdessä is an adverb meaning “together”. It is fairly flexible in word order, but typically it appears near the verb or at the end of the clause.

All of these are natural:

Torstai-iltana katsomme yhdessä elokuvaa kotona.
Torstai-iltana katsomme elokuvaa yhdessä kotona.
Torstai-iltana katsomme elokuvaa kotona yhdessä. (your version)

Subtle differences:

katsomme yhdessä elokuvaa – slightly more emphasis on doing the watching together.
ending with yhdessä often makes “together” feel a bit more emphatic in speech.

If you put Yhdessä at the very beginning—Yhdessä katsomme elokuvaa kotona.—it strongly emphasizes togetherness (“Together, we watch a movie at home”), which might sound a bit dramatic in some contexts.

How flexible is the word order in this sentence? For example, can I say Katsomme elokuvaa yhdessä kotona torstai-iltana?

Yes, Finnish word order is quite flexible, and your alternative is grammatical:

Katsomme elokuvaa yhdessä kotona torstai-iltana.

Typical “neutral” orders for this sentence could be:

Torstai-iltana katsomme elokuvaa kotona yhdessä. (time first)
Katsomme elokuvaa torstai-iltana kotona yhdessä.
Katsomme elokuvaa yhdessä kotona torstai-iltana.

In Finnish, word order is used a lot for information structure and emphasis:

The first element often carries topic or focus.
- Torstai-iltana katsomme… – “As for Thursday evening, we watch…”
- Kotona katsomme… – “At home we watch…” (contrast with somewhere else)

However, the basic meaning (who does what, when, where, how) stays the same in all these versions. As long as you keep the verb forms and case endings correct, you can rearrange elements fairly freely.