Siis kokous alkaa huomenna?

In this sentence, siis does not mean a literal therefore/so in a formal logical sense. In conversation, it often works as a discourse word like:

• so
• right
• wait, so...
• oh, so...

Here it adds a sense of checking, realizing, or confirming something. The speaker may be thinking:

• Oh, so the meeting starts tomorrow?
• So the meeting starts tomorrow, then?

It often gives the sentence a slightly conversational or reactive tone.

Finnish can make a yes/no question simply by using question intonation in speech and a question mark in writing.

So:

• Kokous alkaa huomenna. = a statement
• Siis kokous alkaa huomenna? = a question, often asking for confirmation

This is similar to English sentences like:

• You’re leaving tomorrow?
• So the meeting starts tomorrow?

It sounds natural especially when the speaker is checking information rather than asking a completely neutral question.

There could be one, but it is not required in this kind of conversational confirmation question.

A more explicit yes/no question would be:

• Alkaako kokous huomenna?

That is a straightforward Does the meeting start tomorrow?

But:

• Siis kokous alkaa huomenna?

feels more like:

• Oh, so the meeting starts tomorrow?
• Let me check: the meeting starts tomorrow?

So the version without -ko/-kö is often more conversational and can sound like the speaker is reacting to something just said or inferred.

Yes. Both are correct, but they are used a bit differently.

• Alkaako kokous huomenna?
  = a normal, direct yes/no question

• Siis kokous alkaa huomenna?
  = a confirmation question, often with a sense of so... is that right?

The second one may suggest that:

• the speaker has just learned this,
• the speaker is surprised,
• the speaker is checking they understood correctly.

So the difference is mostly in tone and conversational function, not basic meaning.

Finnish often uses the present tense to talk about the future when the time is clear from context.

Here, huomenna already shows that the event is in the future, so alkaa stays in the present:

• Kokous alkaa huomenna.

This is very normal in Finnish, just like in English sentences such as:

• The meeting starts tomorrow.

So there is no special future tense needed here.

Finnish has no articles like a/an/the.

So kokous can mean:

• a meeting
• the meeting

Which one is meant depends on context.

In this sentence, the meaning is probably the meeting, because both speaker and listener already know which meeting they are talking about. Finnish normally leaves that to context instead of adding an article.

Kokous is in the nominative form, which is the basic dictionary form.

It is nominative here because it is the subject of the sentence:

• kokous = the meeting
• alkaa = starts
• huomenna = tomorrow

So structurally it is very simple:

• The meeting
  • starts
    • tomorrow

Huomenna is the usual adverb meaning tomorrow.

Historically, it is related to an old case form, but for learners it is best to treat it simply as a fixed time adverb. You use it as a whole word to mean tomorrow.

Examples:

• Nähdään huomenna. = See you tomorrow.
• Lähden huomenna. = I’m leaving tomorrow.

So in this sentence, huomenna tells us when the meeting starts.

Yes, but not as rigidly as in English.

The order:

• Siis kokous alkaa huomenna?

sounds natural for a conversational confirmation question.

If you say:

• Alkaako kokous huomenna?

the verb comes first because of the question particle -ko attached to the verb.

Without -ko/-kö, Finnish often keeps statement-like word order and lets intonation/context show that it is a question.

So the word order here helps the sentence feel like:

• a reaction,
• a check,
• a clarification.

It often sounds like the speaker is:

• confirming information,
• slightly surprised,
• making sure they understood correctly,
• reacting to something just said.

Depending on voice and context, it could mean things like:

• So the meeting starts tomorrow?
• Wait, the meeting starts tomorrow?
• Right, so the meeting starts tomorrow?

So this is not just a neutral information question. It usually has a conversational, reactive tone.

Siis is pronounced with a long ii sound.

Roughly:

• siis = one long vowel, not two separate syllables

A simple approximation for English speakers is something like sees, but with Finnish pronunciation:

• s is always a clear s
• ii is long
• the final s is clear and voiceless

The long vowel matters in Finnish, so siis should sound longer than a short si would.