Three subordinating conjunctions divide up the territory of cause and time. koska answers "why?" — it gives the reason. kun answers "when?" — it marks time, and in speech it can soften into a light "since/because". kunnes marks an endpoint — "until". They look and sound similar, and one of them, kun, sits one single vowel away from the completely unrelated comparison word kuin. This page keeps them straight.
koska: "because" (cause)
koska introduces the reason for something. It answers the question miksi? ("why?"). The clause it heads can come after the main clause or before it.
Tulin, koska halusin.
I came because I wanted to.
En voinut nukkua, koska naapurit pitivät melua.
I couldn't sleep because the neighbours were making noise.
Koska sää oli huono, jäimme sisälle.
Because the weather was bad, we stayed inside.
kun: "when / as" (time)
kun is the everyday time conjunction: "when", "as", "once". It marks that one event happens at the time of another — either a single past event or a recurring/simultaneous one.
Kun sataa, jään kotiin.
When it rains, I stay home.
Kun olin nuori, asuin maalla.
When I was young, I lived in the countryside.
Soita minulle, kun pääset perille.
Call me when you get there.
Kun saavuin asemalle, juna oli jo lähtenyt.
When I arrived at the station, the train had already left.
Notice the range: habitual ("when it rains, I…"), a past state ("when I was young"), a future point ("when you get there"), and a single past moment ("when I arrived"). kun covers them all — it is the general-purpose "when" of subordinate clauses.
kun as a soft "because"
In speech, kun also does a job that overlaps with koska: it can introduce a reason, with a softer, more conversational feel than the flat koska. This is (informal) and very common.
Jäin kotiin, kun oli niin kylmä.
I stayed home, since it was so cold.
En ehtinyt syödä, kun oli niin kiire.
I didn't have time to eat, as it was so hectic.
Because kun can mean both "when" and "because", it is occasionally ambiguous — which is exactly why careful writing prefers koska when the meaning is purely causal. If a reader might mishear your "since" as "at the time when", switch to koska. The finer choice is treated on kun vs koska.
kunnes: "until" (endpoint)
kunnes marks the endpoint of an action: it keeps going until the moment named in the clause. It answers "until when?"
Odota, kunnes tulen.
Wait until I come.
Jatkoin lukemista, kunnes silmät väsyivät.
I kept reading until my eyes got tired.
Hän juoksi, kunnes ei jaksanut enää.
He ran until he couldn't go on any longer.
Do not stretch koska or kun to mean "until" — that endpoint sense belongs to kunnes alone. (For "before", Finnish uses a separate conjunction; see ennen kuin.)
The trap: kun is not kuin
This is the error to burn into memory. kun ("when") and kuin ("than / as", the comparison word) differ by a single vowel, i — but they are entirely different conjunctions doing entirely different jobs.
| Word | Meaning | Example |
|---|---|---|
| kun | "when / as" (time) | Kun sataa, jään kotiin. |
| kuin | "than / as" (comparison) | Hän on pidempi kuin minä. |
Hän on pidempi kuin minä.
He is taller than me. (comparison → kuin)
Juoksen niin nopeasti kuin voin.
I run as fast as I can. (comparison → kuin)
Kun juoksin, satoi.
When I was running, it was raining. (time → kun)
Because the only visible difference is that one letter, both native writers and learners slip — but the meanings do not overlap at all. If you are comparing two things ("taller than", "as fast as"), it is kuin. If you are locating something in time ("when"), it is kun. The split is drilled further on kuin vs kun.
How this differs from English
English keeps "because", "when", and "until" as three obviously different words, so the concepts are familiar — the difficulty is purely that Finnish's forms are so close to each other (kun / kuin / kunnes / koska all start alike). The extra wrinkle English does not prepare you for is that kun can also mean "because" in speech, and that koska doubles as the question word "when?". Keep the core jobs anchored — koska = why, kun = when, kunnes = until, kuin = than — and let context handle the overlaps.
Common Mistakes
❌ Hän on pidempi kun minä.
Incorrect — comparison needs kuin, not kun.
✅ Hän on pidempi kuin minä.
He is taller than me.
❌ Odota, koska tulen. (meaning 'until')
Incorrect — 'until' is kunnes, not koska.
✅ Odota, kunnes tulen.
Wait until I come.
❌ Koska sataa, jään kotiin. (meaning 'when it rains')
Incorrect for habitual 'when' — koska says 'because'; use kun.
✅ Kun sataa, jään kotiin.
When it rains, I stay home.
❌ Juoksen niin nopeasti kun voin.
Incorrect — 'as fast as' is a comparison, so it takes kuin.
✅ Juoksen niin nopeasti kuin voin.
I run as fast as I can.
Key Takeaways
- koska = "because" (reason); also the question word "when?" in questions.
- kun = "when / as" (time), and a soft (informal) "because" in speech.
- kunnes = "until" (endpoint) — nothing else covers this sense.
- kuin = "than / as" (comparison), one vowel from kun but a different word entirely.
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Start learning Finnish→Related Topics
- kun vs koskaA2 — How to choose kun (temporal 'when, as') over koska (causal 'because') — the time-vs-cause split that English 'when/since' hides.
- kuin vs kunB2 — The comparison word kuin ('than, as') versus the temporal kun ('when') — a one-letter difference that spoken Finnish hides but writing demands.
- Condition and Concession: jos, vaikka, jottaB1 — How Finnish builds if-clauses (jos), even-though clauses (vaikka), and purpose clauses (jotta) — and why jos never means 'whether'.
- Temporal Clauses: ennen kuin, sen jälkeen kun, kunnesB1 — The multi-word temporal connectives — ennen kuin (before), sen jälkeen kun (after), heti kun (as soon as), kunnes (until) — and the kuin/kun trap inside them.