Learn Hardcore Finnish: Usein puhelin unohtuu lipaston laatikkoon, kun tulen kotiin väsyneenä. - Often the phone gets forgotten in the drawer of the chest of drawers when I come home tired.

Usein puhelin unohtuu lipaston laatikkoon… (neutral, very common)
Puhelin usein unohtuu lipaston laatikkoon… (also natural; a bit more focus on puhelin)
Puhelin unohtuu usein lipaston laatikkoon… (focus shifts slightly toward the forgetting event)

All of these are grammatical. Word order in Finnish mainly affects emphasis and information structure, not basic meaning, so usein is fairly free to move among the early positions in the clause.

Why is puhelin in the basic (nominative) form and not something like puhelimen?

Puhelin is the grammatical subject of the sentence, so it appears in the nominative:

Puhelin unohtuu… = The phone gets forgotten…

If we used puhelimen, that is the genitive form and normally marks an object or possession, e.g.:

Unohdan puhelimen. = I forget the phone.

In the given sentence, the phone is not the object of someone’s deliberate forgetting; instead, it is the thing that ends up forgotten, so it is the subject and stays in the nominative: puhelin.

What exactly is unohtuu, and how is it different from unohdan or unohtaa?

There are two related verbs:

unohtaa = to forget (transitive; someone forgets something)
unohtua = to be forgotten, to get forgotten, to end up forgotten (intransitive; something ends up forgotten)

Unohtuu is the 3rd person singular present form of unohtua:

Puhelin unohtuu. = The phone gets forgotten.

Compare:

Unohdan puhelimen lipaston laatikkoon.
I forget the phone in the drawer of the dresser. (I am clearly the one to blame.)
Puhelin unohtuu lipaston laatikkoon.
The phone gets forgotten in the drawer of the dresser. (More impersonal; it ends up left there.)

So unohtuu avoids explicitly saying who does the forgetting. This is very natural in Finnish for accidental or habitual situations.

Is unohtuu a passive form?

No. It looks a bit like a passive to English speakers, but it is not the Finnish passive.

unohtuu is 3rd person singular of the intransitive verb unohtua.
The Finnish passive would be unohdetaan (from unohtaa), e.g.
Puhelin unohdetaan lipaston laatikkoon. = The phone is (habitually) forgotten / people forget the phone…

So:

unohtuu ≈ gets forgotten, ends up forgotten (no agent expressed, more about the state/result)
unohdetaan ≈ is forgotten / people forget (true passive or impersonal subject)

How is lipaston laatikkoon built, and what does each word do?

Lipaston laatikkoon literally breaks down as:

lipasto = a chest of drawers / dresser
lipaston = genitive of lipasto → of the dresser
laatikko = drawer, box
laatikkoon = illative of laatikko → into the drawer

So lipaston laatikkoon means:

into the drawer of the dresser / into the dresser drawer

Structure: [Owner in genitive] + [thing in a local case]

This pattern is very common:

auton oviin = into the car’s doors
pöydän alle = under the table
talon katolle = onto the house’s roof

Why is laatikkoon in that particular case, and how can I recognize it?

Laatikkoon is in the illative case, which usually indicates movement into something.

Basic form: laatikko
Illative: laatikkoon (double k + -on ending)

Meaning:

laatikko = drawer
laatikkoon = into the drawer

Other local cases for comparison:

laatikossa = in the drawer (static location, inessive)
laatikosta = out of the drawer (elative)

In the sentence, the phone ends up inside the drawer, so the illative laatikkoon is required.

Why is there a comma before kun?

Kun introduces a subordinate clause meaning when. In standard written Finnish, you normally use a comma before such clauses:

…, kun tulen kotiin väsyneenä.
…, when I come home tired.

This is a general rule: a main clause followed by a kun, että, joka, koska, etc. clause usually has a comma before the conjunction.

You could also switch the order:

Kun tulen kotiin väsyneenä, puhelin unohtuu lipaston laatikkoon.

The comma remains, now after the kun-clause instead of before it.

Why is it kun tulen kotiin and not kun minä tulen kotiin?

In Finnish, personal pronouns are often omitted when the verb ending already tells you who the subject is.

tulen = I come
The ending -n marks 1st person singular.

So:

(Minä) tulen kotiin.
Both forms are grammatically correct, but the version without minä is more neutral and common in this kind of sentence.

You would include minä if you really want to emphasize I, for example in contrast:

Kun minä tulen kotiin, puhelin unohtuu; kun sinä tulet kotiin, se ei unohdu.
When I come home, the phone is forgotten; when you come home, it isn’t.

Why is it kotiin and not koti or kotona?

Kotiin is the illative form of koti and indicates movement towards home:

koti = home (basic form)
kotiin = to home, into home (movement)
kotona = at home (static location)

So:

Tulen kotiin. = I come home.
Olen kotona. = I am at home.

In the sentence, you are going home, not just being at home, so the directional form kotiin is required.

What form is väsyneenä, and what does it add to the meaning?

Väsyneenä is the essive case of the adjective väsynyt (tired).

väsynyt = tired (basic form)
väsyneenä = being tired / in a tired state

The essive often expresses a temporary state or role during an action:

Tulen kotiin väsyneenä.
I come home (while) tired / in a tired state.

So the meaning is that at the time you are coming home, you are tired. It’s not describing a permanent trait but your condition at that moment.

Could the word order be kun tulen väsyneenä kotiin? Would that change the meaning?

Yes, kun tulen väsyneenä kotiin is also grammatical and means essentially the same thing:

kun tulen kotiin väsyneenä
kun tulen väsyneenä kotiin

Both convey when I come home tired.

The difference is only a slight shift in rhythm and emphasis; Finnish allows relatively free word order in adverbials like this. The safest, most neutral version is usually the one in the original sentence, kotiin väsyneenä, but the alternative is natural as well.

Why is it puhelin unohtuu and not minä unohdan puhelimen if I am the one forgetting it?

Both are possible, but they have different focus:

Minä unohdan puhelimen lipaston laatikkoon.
Focus on me as the agent: I forget the phone in the drawer. Very direct; can sound like you are taking clear responsibility or describing a specific incident.
Puhelin unohtuu lipaston laatikkoon.
Focus on the phone and the result: The phone (often) ends up forgotten in the drawer.
This is more impersonal and suits habitual, slightly accidental situations.

In everyday Finnish, people often choose unohtua when they want to talk about something happening without emphasizing blame or agency: the situation just tends to happen.