Learn Hardcore Finnish: Varovaisuus on tärkeä asia kotona ja koulussa. - Caution is an important thing at home and at school.

It is formed from the adjective varovainen (careful) using the abstract-noun suffix -uus / -yys, which often means “-ness” or “-ity” in English:

varovainen = careful
varovaisuus = carefulness, the quality of being careful

So in the sentence, Varovaisuus is a noun and acts as the subject: “Carefulness / Being careful is …”

Why is on used here—could the sentence work without it?

On is the 3rd person singular of the verb olla (to be), so it means “is”.

In standard Finnish, you normally must include on in sentences of the type “X is Y”:

Varovaisuus on tärkeä asia. = Carefulness is an important thing.

You can only drop on in very informal speech under certain conditions (especially when it would be olisi “would be”), but in normal written or taught Finnish you keep it. So here, the sentence does not work correctly without on.

Why do we say tärkeä asia instead of just tärkeä?

Literally:

tärkeä = important (adjective)
asia = thing, matter, issue

Finnish often uses asia to make a more concrete noun phrase:

tärkeä asia = “an important thing / an important matter”

This is a very common pattern:

Tämä on tärkeä asia. = This is an important matter.
Turvallisuus on tärkeä asia. = Safety is an important issue.

You could describe carefulness without asia, for example:

Varovaisuus on tärkeää. = Carefulness is important.

Both are correct. With “tärkeä asia” you sound more like you’re talking about an important topic/issue, not just describing a property in the abstract.

Why is tärkeä in this basic form and not tärkeää?

The form of tärkeä depends on what it is describing.

In this sentence:

tärkeä modifies asia: tärkeä asia = an important thing
asia is in the basic (nominative) form, so tärkeä is also nominative singular.

If you drop asia and just say:

Varovaisuus on tärkeää.

then tärkeää is in the partitive. With abstract or “mass-like” subjects (like carefulness, love, water), Finnish very often uses a partitive predicate to say “X is Y” in a general way:

Vesi on kylmää. = Water is (some) cold. → Water is cold.
Rakkaus on tärkeää. = Love is important.

So:

Varovaisuus on tärkeä asia. → adjective agrees with asia (nominative).
Varovaisuus on tärkeää. → adjective is in partitive, describing an abstract quality directly.

Could we also say Varovaisuus on tärkeää kotona ja koulussa? If yes, what’s the difference?

Yes, that sentence is completely correct:

Varovaisuus on tärkeää kotona ja koulussa.
Carefulness is important at home and at school.

Differences:

Varovaisuus on tärkeä asia kotona ja koulussa.
Sounds like: “Carefulness is an important matter/issue at home and at school.”
Slightly more concrete, like you’re treating it as a topic or point on a list.
Varovaisuus on tärkeää kotona ja koulussa.
More directly describes the quality: “Being careful is important at home and at school.”
This is often the more neutral, everyday way to say it.

Both are natural; it’s a nuance of style rather than a big change in meaning.

What exactly does asia mean here? Is it necessary?

Asia is a very general word meaning:

thing, matter, issue, affair, point, depending on context.

In this sentence:

tärkeä asia ≈ “an important matter / an important thing”

It is not strictly necessary for the meaning. You can remove it:

Varovaisuus on tärkeää kotona ja koulussa.

Using asia:

makes the language sound a bit more school‑like, explanatory, or formal, as if the speaker is saying “this is an important point we should remember.”

Omitting asia makes the sentence shorter and a bit more direct.

What case are kotona and koulussa, and how do they differ in meaning from plain koti and koulu?

Base forms:

koti = home
koulu = school

In the sentence:

kotona = at home
koulussa = at / in school

Grammatically:

koulussa is the inessive case of koulu (inside / in / at something):
koulu → koulussa (in / at school)
kotona is a special locative form of koti that means “at home”.
Instead of the regular -ssa, koti has its own set of irregular local forms:
- kotona = at home
- kotiin = (to) home
- kotoa = from home

So:

koti = home (as a bare noun)
kotona = at home
koulu = school
koulussa = in/at school

Why does koti become kotona but koulu becomes koulussa? Why not kotissa?

This is because koti is irregular in its local (place) forms.

For most nouns, “in/at X” is formed with -ssa / -ssä:

talo → talossa = in the house
kauppa → kaupassa = in the shop
koulu → koulussa = in/at school

But koti is special. Its standard local forms are:

kotona = at home
kotiin = (to) home
kotoa = from home

You do not normally say *kotissa. Instead, you memorize kotona/kotiin/kotoa the same way you memorize irregular prepositional phrases in English like “at home” (not “in home”).

So:

✔ kotona
✖ *kotissa (not used in standard Finnish)

Could we say kodissa instead of kotona? Would that change the meaning?

Kodissa does exist, but it is less common and has a slightly different nuance.

kotona = at home (the default, very common, neutral expression)
kodissa = in the home (more literally in the home, often more formal or emphasizing the home as a physical or social environment)

For everyday speech, in a sentence like this one, Finns almost always say:

Varovaisuus on tärkeää kotona. (or …tärkeä asia kotona.)

Using kodissa here would sound marked or stylistic, as if you were writing a sociological text about “in the home” as an institution. So for learners, stick with kotona in this kind of sentence.

Can kotona ja koulussa go at the beginning of the sentence: Kotona ja koulussa varovaisuus on tärkeä asia?

Yes, that word order is perfectly correct:

Kotona ja koulussa varovaisuus on tärkeä asia.

Word order in Finnish is fairly flexible, especially for placing time and place expressions at the beginning for emphasis or context.

The differences are mainly in emphasis:

Varovaisuus on tärkeä asia kotona ja koulussa.
Neutral: talks about carefulness, then adds where it is important.
Kotona ja koulussa varovaisuus on tärkeä asia.
Emphasis slightly shifts to those places: “At home and at school, carefulness is an important thing.”

Why are there no words for a/an/the (“an important thing”) in this Finnish sentence?

Finnish has no articles (no equivalent of a, an, the).

So:

tärkeä asia can mean:
- an important thing
- the important thing
- just important thing (when the English article is not needed)

Which one is meant depends on context, not on a separate word. Here, tärkeä asia naturally reads as “an important thing / an important matter” because we’re talking about carefulness in general, not about a single, already-known “important thing.”

How would you literally translate the whole sentence word by word?

A close word‑for‑word breakdown is:

Varovaisuus = carefulness / being‑careful
on = is
tärkeä = important
asia = thing / matter / issue
kotona = at‑home
ja = and
koulussa = in‑school / at‑school

So a very literal rendering would be:

“Carefulness is [an] important thing at‑home and in‑school.”

Natural English:

“Carefulness is important at home and at school.”
or
“Being careful is an important thing at home and at school.”