Learn Hardcore Finnish: Jätän takin toimistoon, koska siellä on lämmin. - I leave the coat at the office because it is warm there.

Jätän is the 1st person singular present tense of jättää (minä jätän = I leave / I’m leaving). Finnish often uses the present tense for near-future intentions too, so depending on context it can also feel like I’ll leave my coat (at the office).

Why is taki in the form takin and not takki or takkia?

Takin is the “total object” form (often called accusative, but it looks like the genitive -n here). It’s used when the action is seen as complete/bounded: you’re leaving the coat (as a whole) there.

Jätän takin… = I leave the coat (as a complete item, a definite act)
Jätän takk ia… (partitive) would suggest an unbounded/ongoing/indefinite idea (often odd here), like “I’m leaving some coat / leaving the coat around” or emphasizing incompleteness/indefiniteness.

How do we get toimistoon from toimisto, and what case is it?

Toimistoon is the illative case, meaning into / to (inside) the office.

Formation here:

toimisto → toimistoon
For many words ending in -o/-ö, illative is -oon/-öön (with vowel lengthening): talo → taloon, toimisto → toimistoon.

What’s the difference between toimistoon and toimistossa?

toimistoon (illative) = movement/direction into/to the office
toimistossa (inessive) = location in/at the office

So:

Jätän takin toimistoon = I leave the coat in there (you place it there)
Jätän takin toimistossa = I leave the coat while I’m at the office (less likely meaning)

Why is there a comma before koska?

In Finnish, a subordinate clause is typically separated by a comma. Koska introduces a reason clause, so:

Jätän takin toimistoon, koska siellä on lämmin.

This comma is standard and expected in neutral writing.

Does koska always mean because, and can it appear elsewhere in the sentence?

Most commonly koska = because. It can also mean since (in the causal sense). The koska-clause can come first or second:

Jätän takin toimistoon, koska siellä on lämmin.
Koska siellä on lämmin, jätän takin toimistoon. (more emphasis on the reason)

What exactly is siellä, and do we need it?

Siellä means there (in that place). It points back to toimisto (the office) without repeating it.

You can omit it if the reference is obvious, but Finnish often likes to include a place adverb:

…koska siellä on lämmin. = because it’s warm there
…koska on lämmin. = because it’s warm (more general; can sound less specific)

You could also replace it with a case form of toimisto:

…koska toimistossa on lämmin. = because it’s warm in the office

Why is it on lämmin and not se on lämmin?

Finnish can express weather/conditions without a dummy subject like English it. So on lämmin is a normal way to say it’s warm (in a place / generally).

Se on lämmin is possible, but it usually points to a specific thing already mentioned (like the room or the coat) rather than just stating conditions.

I’ve seen on lämmintä too. What’s the difference between on lämmin and on lämmintä?

Both can be used, but the nuance differs:

Siellä on lämmin. = It’s warm there (more “adjective-style,” like describing the place’s condition)
Siellä on lämmintä. = It’s warm there (partitive; often very natural for weather/ambient conditions, like “there is warmth”)

In everyday Finnish, Siellä on lämmintä is extremely common for “it’s warm (in there).”

Can the word order change, and what does it affect?

Yes—Finnish word order is flexible and often signals emphasis/focus:

Jätän takin toimistoon, koska siellä on lämmin. (neutral)
Takin jätän toimistoon, koska siellä on lämmin. (emphasis: the coat specifically)
Toimistoon jätän takin… (emphasis: to the office as the place)

The basic meaning stays, but what feels “highlighted” changes.

How does lämmin inflect in other cases? It doesn’t look like lämpim- but I’ve seen that.

Lämmin has a stem change in many forms:

nominative: lämmin
genitive: lämpimän
partitive: lämmintä
inessive: lämpimässä
comparative: lämpimämpi

So seeing lämpim- is normal; it’s the inflectional stem used in many case forms.