Learn Hardcore Finnish: Sinun pitäisi puhua kollegan kanssa, jos olet pettynyt palkkaan. - You should talk with a colleague if you are disappointed with the salary.

In this structure, Finnish uses the genitive form of the pronoun (sinun, not sinä) with the verb pitää in the conditional (pitäisi):

Minun pitäisi… – I should…
Sinun pitäisi… – You should…
Hänen pitäisi… – He / she should…

So sinun is grammatically genitive, but you can simply think of “Sinun pitäisi” as the normal way to say “you should” in Finnish.
Using “Sinä pitäisi” is wrong in standard Finnish.

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

Pitäisi is the conditional form of the verb pitää (“to have to / must” in this construction).

sinun pitää puhua – you have to talk / you must talk
sinun pitäisi puhua – you should talk / you ought to talk

So:

pitää → strong obligation (must)
pitäisi → softer, more polite suggestion (should)

The conditional ending -isi on pitäisi corresponds roughly to English “would / should”.

Is “pitäisi” always the same form, even for different persons (I, you, they)?

Yes, in this construction pitäisi does not change with person. The pronoun in the genitive shows who should do it:

Minun pitäisi puhua – I should talk
Sinun pitäisi puhua – You should talk
Meidän pitäisi puhua – We should talk
Heidän pitäisi puhua – They should talk

The verb stays pitäisi in all of those. Only the pronoun changes.

Why is it “puhua” and not a conjugated form like “puhut”?

After pitää / pitäisi (in the meaning must / should), Finnish uses the basic infinitive of the main verb:

sinun pitäisi puhua – you should talk
minun pitää mennä – I must go
meidän pitäisi kysyä – we should ask

So the pattern is:

[genitive pronoun] + pitää / pitäisi + [infinitive]

You cannot say “sinun pitäisi puhut”; that’s incorrect.

Why is it “kollegan kanssa” and not “kollega kanssa”?

The postposition kanssa (“with”) requires its complement to be in the genitive case:

ystävä → ystävän kanssa – with a friend
opettaja → opettajan kanssa – with a teacher
kollega → kollegan kanssa – with a colleague

So kollegan is the genitive singular of kollega.
Think: “the with of colleague” → “with (a) colleague”.

Does “kollegan kanssa” mean “with your colleague” or “with a colleague”?

Finnish has no articles, so kollegan kanssa is ambiguous and can mean:

with a colleague
with the colleague
with your colleague

Context decides what is meant.
If you want to be explicit about “your colleague”, you can say:

puhua kollegasi kanssa – talk with your colleague

Here kollegasi means “your colleague” (the -si is a possessive suffix).

How would I say “with colleagues” in plural?

Use the plural genitive before kanssa:

kollegat (nominative, plural)
kollegoiden / kollegojen (genitive, plural)

So:

puhua kollegoiden kanssa – to talk with colleagues

Both kollegoiden and kollegojen are accepted genitive plural forms.

Why is there a comma before “jos”?

In Finnish, a comma normally separates a main clause and a subordinate clause (like an if-clause).

Sinun pitäisi puhua kollegan kanssa, (main clause)
jos olet pettynyt palkkaan. (subordinate “if”-clause)

You also need a comma if you put the jos-clause first:

Jos olet pettynyt palkkaan, sinun pitäisi puhua kollegan kanssa.

So the comma is a regular rule of Finnish punctuation, not optional.

What does “jos” mean here, and could I use “kun” instead?

Jos means “if”:

jos olet pettynyt palkkaan – if you are disappointed with your salary

Kun normally means “when” (in the sense of “at the time that”):

kun olet pettynyt palkkaan – when(ever) you are disappointed with your salary

In your sentence we are talking about a condition (“if this happens, then do that”), so jos is the natural and correct choice.
Kun would sound like you’re describing a repeated or known situation, not a conditional one.

Why is it “olet pettynyt” instead of something like a single verb “petyt”?

Finnish often expresses states like “disappointed” with olla (“to be”) + a participle:

olla pettynyt johonkin – to be disappointed in/with something

So:

olet pettynyt – you are disappointed
olin pettynyt – I was disappointed
olemme pettyneitä – we are disappointed (plural form of the participle)

There is a verb pettyä (“to become disappointed”), for example:

Petyn helposti. – I (tend to) get disappointed easily.
Petyt, jos odotat liikaa. – You will be disappointed if you expect too much.

But in your sentence the focus is on your current state (“if you are disappointed”), so olet pettynyt is used.

Why is it “palkkaan” and not just “palkka”?

Palkkaan is the illative case of palkka (“salary, pay”):

palkka – salary (basic form)
palkkaan – into / in the salary (grammatically “into salary”)

The adjective pettynyt (from pettyä) usually takes the illative case:

pettynyt tulokseen – disappointed with the result
pettynyt peliin – disappointed with the game
pettynyt palkkaan – disappointed with the salary

So palkkaan is required by the way pettynyt works; it’s not arbitrary.

Can I say “palkkaasi” to mean “your salary”?

Yes. Palkkaasi is palkka + possessive suffix -si (“your”) in the illative:

palkka → palkkaasi – into your salary / in your salary (here: “with your salary”)

So you could say:

…jos olet pettynyt palkkaasi. – …if you are disappointed with your salary.

Both:

pettynyt palkkaan
pettynyt palkkaasi

are acceptable, but palkkaasi makes it explicit that we mean your salary.

Can I change the word order and start with the “if”-clause?

Yes. Both orders are natural:

Sinun pitäisi puhua kollegan kanssa, jos olet pettynyt palkkaan.
Jos olet pettynyt palkkaan, sinun pitäisi puhua kollegan kanssa.

The meaning stays the same; only the emphasis changes slightly:

First version: focuses first on what you should do.
Second version: starts by presenting the condition.

What is the informal spoken version of “Sinun pitäisi puhua kollegan kanssa”?

In everyday speech, Finns often shorten pronouns and verbs:

Sinun → sun
pitäisi → pitäis

So you will commonly hear:

Sun pitäis puhua kollegan kaa, jos oot pettyny palkkaan.

Notice also spoken-style reductions:

kanssa → kaa
olet → oot
pettynyt → pettyny

These are informal but very common in speech.