Learn Hardcore Finnish: Sinun pitäisi mainita tämä asia kokouksessa. - You should mention this matter in the meeting.

In Finnish, with the verb pitää in the “must / should” meaning, the person who has the obligation is put in the genitive, and pitää / pitäisi stays in 3rd person singular:

Minun pitää mennä. – I have to go.
Sinun pitää mennä. – You have to go.
Meidän pitää mennä. – We have to go.

In the conditional (for “should”), you get:

Minun pitäisi mainita... – I should mention...
Sinun pitäisi mainita... – You should mention...

So sinä pitäisit mainita is not how Finnish expresses “you should mention”; you need the genitive sinun plus pitäisi.

What exactly does pitäisi mean here, and why is it in that form?

Pitäisi is the conditional form of pitää in the “have to / must” sense.

pitää (present) ≈ “must, have to”
pitäisi (conditional) ≈ “should, ought to”

So:

Sinun pitää mainita tämä asia kokouksessa.
≈ You have to / must mention this thing in the meeting.
Sinun pitäisi mainita tämä asia kokouksessa.
≈ You should mention this thing in the meeting. (softer, more like a recommendation)

The conditional ending -isi is what makes it “should” rather than “must”.

What’s the difference between Sinun pitää mainita... and Sinun pitäisi mainita...?

Nuance of obligation:

Sinun pitää mainita tämä asia kokouksessa.
Stronger: this is a requirement.
→ You must / have to mention it.
Sinun pitäisi mainita tämä asia kokouksessa.
Softer, advisory: it’s recommended or expected.
→ You should mention it.

In everyday speech:

Rules, instructions, deadlines → pitää
Advice, polite suggestions, “it would be good if...” → pitäisi

Why is it mainita and not something like mainitset?

Mainita is the basic infinitive form (“to mention”).

With verbs like pitää / pitäisi, Finnish uses the infinitive for the following verb:

Sinun pitäisi mennä. – You should go.
Sinun pitäisi syödä. – You should eat.
Sinun pitäisi mainita tämä asia. – You should mention this thing.

If you conjugate mainita instead, you’re saying a different sentence:

Sinä mainitset tämän asian kokouksessa. – You (will) mention this thing in the meeting.

So:

Sinun pitäisi mainita... = “you should mention...”
Sinä mainitset... = “you mention / will mention...”

The personal information (who is doing it) is already carried by sinun + pitäisi, so mainita stays in the infinitive.

What case is tämä asia in, and why isn’t it tämän asian?

In the example tämä asia is in the nominative form.

Grammatically, it functions as the object of mainita, but because it’s inside a pitää/pitäisi + infinitive structure, Finnish typically uses the nominative form for that object:

Sinun pitäisi mainita tämä asia kokouksessa.

If you make a simple main‑clause sentence without pitäisi, you’ll see a different form:

Mainitset tämän asian kokouksessa.
(“You will mention this thing in the meeting.”)

Here tämän asian is the usual “total object” form (often called genitive/accusative).

For now, as a learner, the safe rule in this type of sentence is:

With [genitive pronoun] + pitää/pitäisi + infinitive, keep the object in nominative:
Sinun pitäisi mainita tämä asia...

What case is kokouksessa, and what does the ending -ssa mean?

Kokouksessa is in the inessive case, marked by -ssa / -ssä, which usually means “in / inside / at”.

kokous – a meeting
kokouksessa – in the meeting, at the meeting

Compare with other local cases:

kokoukseen (illative, into the meeting)
kokouksesta (elative, out of/from the meeting)

In this sentence, kokouksessa answers “where should you mention it?” → in/at the meeting.

Can I change the word order, for example: Kokouksessa sinun pitäisi mainita tämä asia?

Yes. Finnish word order is fairly flexible, and different orders change the emphasis, not the basic meaning.

Some common variants:

Sinun pitäisi mainita tämä asia kokouksessa.
– Neutral, straightforward: the whole idea as a simple statement.
Kokouksessa sinun pitäisi mainita tämä asia.
– Emphasis shifts to kokouksessa: “In the meeting you should mention this thing (not somewhere else).”
Tämä asia sinun pitäisi mainita kokouksessa.
– Emphasis on tämä asia: “This thing in particular you should mention (maybe others are less important).”

All are grammatically correct; what comes first is usually what the speaker wants to highlight.

Can I leave out sinun and just say Pitäisi mainita tämä asia kokouksessa?

Yes, you can omit sinun, but the meaning becomes less specifically “you” and more impersonal:

Sinun pitäisi mainita tämä asia kokouksessa.
→ Clearly directed at you.
Pitäisi mainita tämä asia kokouksessa.
→ “This thing should be mentioned in the meeting.”
/ “We/one/people should mention this thing in the meeting.”

The second version is common when:

the doer is obvious from context (e.g. everyone in a team), or
the speaker wants to sound less direct and more impersonal.

How would this sentence sound in everyday colloquial spoken Finnish?

A natural colloquial version might be:

Sun pitäis mainita tää asia kokoukses.

Typical changes:

sinun → sun
pitäisi → pitäis
tämä → tää
kokouksessa → kokoukses (final vowel often dropped in speech)

So in casual conversation you’re more likely to hear something like:

Sun pitäis mainita tää asia kokoukses.

How can I make this stronger (“you must”) or softer/more polite in Finnish?

Stronger / more forceful:

Sinun pitää mainita tämä asia kokouksessa.
– You have to / must mention this.
Sinun täytyy mainita tämä asia kokouksessa.
– Very close to “you must”.
Sinun on pakko mainita tämä asia kokouksessa.
– “You are forced / really have to mention this” (very strong).

Softer / more polite suggestions:

Ehkä sinun kannattaisi mainita tämä asia kokouksessa.
– “Maybe it would be a good idea for you to mention this in the meeting.”
Voisit ehkä mainita tämän asian kokouksessa.
– “You could maybe mention this thing in the meeting.”

So pitäisi is already softer than pitää, but you can go even softer with kannattaisi, voisit, etc.

Could I say the same idea using a simple present tense instead of pitäisi?

Yes, but the nuance changes. For example:

Sinä mainitset tämän asian kokouksessa.
– “You will mention this thing in the meeting.”
(sounds like a plan or prediction, not advice)
Mainitsethan tämän asian kokouksessa?
– “You will mention this in the meeting, right?” (checking / requesting)

The original Sinun pitäisi mainita tämä asia kokouksessa. specifically expresses advice / recommendation (“you should…”). Using plain present tense shifts it away from advice toward a statement about what will or should (by arrangement) happen.