Learn Hardcore Finnish: Opettaja on erityisen kiltti, kun olemme tekemässä vaikeaa tehtävää. - The teacher is especially kind when we are in the middle of doing a difficult task.

Here, erityisen is the genitive form of the adjective erityinen, and in Finnish it’s very common for the genitive form of certain adjectives to be used as an intensifier in front of another adjective, almost like “especially / particularly / very”:

erityisen kiltti = especially/particularly kind
erityisen kaunis = especially beautiful
erityisen vaikea = particularly difficult

So:

erityinen opettaja = a special teacher (describes the noun directly)
erityisen kiltti opettaja = an especially kind teacher (intensifies “kind”)

Erityisesti is an adverb (“especially”), but it usually modifies verbs or whole clauses, not another adjective directly, so:

Opettaja on erityisen kiltti. – The teacher is especially kind.
Opettaja auttaa meitä erityisesti silloin, kun tehtävä on vaikea. – The teacher helps us especially when the task is difficult.

Using erityisen before kiltti is the most natural choice here.

Why is it opettaja on kiltti, not something like opettaja on kilt or kilte?

Kiltti is the basic dictionary form of the adjective, and it stays kiltti when used as a predicative (after the verb to be) with a singular subject:

Opettaja on kiltti. – The teacher is kind/nice.
Lapsi on kiltti. – The child is well‑behaved.

Adjectives in Finnish agree in number and case with the noun when they directly modify it:

kiltti opettaja – a kind teacher (both nominative singular)
kiltin opettajan – of the kind teacher (both genitive singular)
kiltit opettajat – kind teachers (both plural nominative)

But when the adjective is used after “on” and just describes the subject (predicative use), and the subject is a singular nominative noun, you also get this basic form:

Opettaja on kiltti.
Opettajat ovat kilttejä. (plural subject → adjective in partitive plural)

So kiltti here is exactly the expected form.

Does kiltti mean “kind” or “well‑behaved”? It sounds like something you’d say about a child.

Kiltti overlaps both meanings, and context decides:

About children / pets: often “well‑behaved, obedient”
- Lapsi on kiltti. – The child is well‑behaved.
About adults: can be “kind, nice, considerate,” but often still with a somewhat soft, gentle nuance, not “heroically kind”:
- Opettaja on kiltti. – The teacher is kind/nice (friendly, gentle, not strict or harsh).

In this sentence, kiltti about a teacher naturally reads as “kind/nice (to us)”, not “obedient.”

If you want a more clearly adult-style word for “kind,” you might also hear:

ystävällinen – friendly, kind
huolehtivainen – caring, considerate

Why is it kun and not koska before olemme tekemässä?

Both kun and koska can be translated as when, but they’re used differently:

kun = when, at the time that
koska = because, since (cause/reason)

In this sentence:

Opettaja on erityisen kiltti, kun olemme tekemässä vaikeaa tehtävää.
→ The teacher is especially kind when we are doing a difficult exercise.

We’re talking about time / situation: at the time when we are doing a difficult task, the teacher is especially kind. So kun is correct.

If you said:

Opettaja on erityisen kiltti, koska olemme tekemässä vaikeaa tehtävää.

that would mean:

The teacher is especially kind *because we are doing a difficult task* (our doing a difficult task is the reason).

So kun = temporal “when” here, not causal.

What does olemme tekemässä literally mean? Is this like the English “we are doing”?

Yes, olemme tekemässä is one of the ways Finnish expresses something similar to the English progressive (“we are in the middle of doing”).

Structure:

olemme = “we are” (1st person plural of olla)
tekemässä = inessive form of the -minen type verb noun from tehdä (“to do”)
- base: tekeminen = “doing” (as a noun)
- tekemässä = “in the doing (of something)”

So olla tekemässä literally has a meaning like “to be in (the state of) doing”.

Semantically, olemme tekemässä ≈ “we are (in the middle of) doing,” with an emphasis that the action is ongoing or in progress at that time:

Olemme tekemässä vaikeaa tehtävää.
→ We are doing a difficult task / in the middle of a difficult task.

Why is it tekemässä and not something like tehdässä? How does this relate to the verb tehdä?

The verb tehdä (“to do, to make”) is irregular and has multiple stems:

dictionary form: tehdä
some forms: tee‑ (e.g. tee! “do!”)
other forms: teke‑ (e.g. tekee, s/he does)
past participle: tehty (done)

The -minen/-massa constructions use the teke‑ stem:

tekeminen – doing (the act of doing)
tekemässä – in the middle of doing
tekemään – going to do

So olemme tekemässä comes from this teke‑ stem, not directly from tehdä as you see it in the dictionary. This is just a built-in irregularity of tehdä that you have to memorize.

Why is vaikeaa tehtävää in the partitive case, not just vaikea tehtävä?

Both words are indeed in the partitive singular:

vaikeaa (partitive of vaikea, “difficult”)
tehtävää (partitive of tehtävä, “task, exercise”)

Reasons for the partitive here:

Partitive object with an ongoing action
- With verbs like olla tekemässä, which express an ongoing / incomplete action, the object is often in the partitive, emphasizing that the action is not finished:
- Olemme tekemässä vaikeaa tehtävää.
  → We’re in the middle of doing it; it’s not yet completed.
Unbounded / not total
- Partitive often marks that you are dealing with part of something, or an action that does not cover the whole of the object. While doing the task, you’re still somewhere within it, not at the end.

If the action were viewed as completed or whole, you might see the genitive (for a total object):

Teimme vaikean tehtävän. – We did the difficult task (finished it).

So partitive here signals: ongoing, not completed work on the task.

What would be the difference if you said vaikean tehtävän instead of vaikeaa tehtävää?

Comparing:

Olemme tekemässä vaikeaa tehtävää.
- partitive vaikeaa tehtävää
- Focus: in the middle of a difficult task. Action is ongoing / incomplete.
Olemme tekemässä vaikean tehtävän.
- genitive vaikean tehtävän
- Grammatically possible, but now much more like:
  We are (about) to complete the difficult task / to get the difficult task done (as a whole).
- It can sound like you are aiming at a definite, whole result (total object), and less like you are just somewhere within the process.

In everyday speech, with olla tekemässä, the partitive is by far more natural for this meaning: in the process of doing a difficult exercise.

Could you just say kun teemme vaikeaa tehtävää instead of kun olemme tekemässä vaikeaa tehtävää?

Yes, you can, and it would still be good Finnish:

Opettaja on erityisen kiltti, kun teemme vaikeaa tehtävää.

Differences in nuance:

kun teemme vaikeaa tehtävää
- Simple present: “when we do / are doing a difficult task.”
- In Finnish, this can refer both to general / habitual situations and to what’s currently happening.
kun olemme tekemässä vaikeaa tehtävää
- More explicitly highlights the ongoing process: “when we are in the middle of doing a difficult task.”

The original version slightly emphasizes the in-progress nature of the activity. In many contexts, though, teemme would be perfectly fine and quite natural.

Does this sentence describe something happening right now or something that usually happens?

In Finnish, the present tense often covers both current and habitual meaning, and context decides which is intended.

Opettaja on erityisen kiltti, kun olemme tekemässä vaikeaa tehtävää.

This can mean:

Right now / this situation
- The teacher is being especially kind while we are doing this difficult exercise (at the moment).
Habitual / general truth
- The teacher is (always) especially kind whenever we’re doing a difficult exercise.

Both readings are possible. With no extra context, many people would understand it as a general habit (“whenever we have hard tasks, our teacher is especially kind”), but the current-situation reading is also grammatically fine.

Could the sentence start with the kun‑clause, and would the comma change?

Yes. In Finnish you can perfectly well place the kun‑clause first:

Kun olemme tekemässä vaikeaa tehtävää, opettaja on erityisen kiltti.

Comma rules:

When the subordinate clause (with kun) comes first, you usually put a comma between the clauses.
When the main clause comes first, you also normally separate them with a comma, as in the original:
- Opettaja on erityisen kiltti, kun olemme tekemässä vaikeaa tehtävää.

So both word orders are correct and natural; the meaning is the same.

What’s the relationship between tehdä, tehtävä, and tehtävä meaning “task”?

All of these share the same root:

tehdä – verb “to do, to make”
tehtävä (verb form) – passive present participle, meaning something like “to be done”
tehtävä (noun) – from that participle, now used as a noun meaning “task, exercise, assignment”

So:

tehtävä literally started out as “(something) to be done” and then became the ordinary word for “task / exercise” (especially in school-book contexts).

In your sentence:

vaikeaa tehtävää = “a difficult task/exercise”
– grammatically: adjective vaikeaa
- noun tehtävää, both partitive singular.