Learn Hardcore Finnish: Kielikerho on vapaaehtoinen.

Finnish often combines nouns like this into one word, so instead of kieli kerho, you get kielikerho. It is in the nominative singular form, acting as the subject of the sentence.

Why is the verb on used here, and what form is it?

On is the 3rd person singular form of the verb olla (to be).

The full conjugation (present tense) of olla starts:

minä olen – I am
sinä olet – you are (singular)
hän on – he/she is
se on – it is

In this sentence, kielikerho is a singular subject, so you use on:
Kielikerho on vapaaehtoinen. = The language club is voluntary.

What part of speech is vapaaehtoinen, and what does it mean?

Vapaaehtoinen is:

an adjective meaning voluntary, optional
and also a noun meaning a volunteer (person), depending on context

In this sentence it is an adjective describing kielikerho:

kielikerho = the thing being described
vapaaehtoinen = what kind of club it is (a voluntary one)

Why is vapaaehtoinen in the same (nominative) form as kielikerho?

In Finnish, when you have a sentence of the type:

[Subject] + on + [adjective/noun]

the adjective/noun that comes after on (called a predicative) usually agrees with the subject in:

number (singular/plural)
case (here: nominative)

So:

Kielikerho on vapaaehtoinen.
– kielikerho: singular nominative
– vapaaehtoinen: singular nominative to match it

If the subject were plural, the adjective would also be plural nominative:

Kielikerhot ovat vapaaehtoisia.
– kielikerhot: plural nominative
– vapaaehtoisia: plural partitive-like form used as plural predicative

Could you say Kielikerho on vapaaehtoista instead? What would that mean?

Normally, Kielikerho on vapaaehtoinen is the standard, neutral way to say The language club is voluntary.

Using vapaaehtoista (partitive singular) would be unusual here and would tend to sound:

incomplete, or
as if you are talking about the quality in a more vague or partial way, not just stating a clear fact

Partitive predicatives appear in certain contexts (e.g. with quantity, incompleteness, changes of state), but for a simple identity statement X is Y, the nominative vapaaehtoinen is correct and natural.

Why doesn’t Finnish use a word for a/the in Kielikerho on vapaaehtoinen?

Finnish generally has no articles like English a, an, the.

Whether kielikerho means a language club, the language club, or just language club depends on context, not on a separate word.

So:

Kielikerho on vapaaehtoinen.
can be translated as:
- The language club is voluntary. (if a specific one is meant)
- A language club is voluntary. (in a more general statement)

The Finnish sentence stays the same; you choose a/the in English depending on what you know about the context.

Is the word order fixed? Could I say Vapaaehtoinen on kielikerho?

The normal, neutral word order here is:

Kielikerho on vapaaehtoinen.
[Subject] – [verb] – [predicative]

Vapaaehtoinen on kielikerho would sound very odd, almost like:

The voluntary one is a language club, where vapaaehtoinen is being treated like a noun (the volunteer/voluntary thing) and kielikerho becomes the predicative.

So for The language club is voluntary, you should keep:

Kielikerho on vapaaehtoinen.

How do you pronounce kielikerho and vapaaehtoinen?

Rough guide using English-like approximations:

kielikerho: KYEH-li-ker-ho
- kie- like kyeh (start like key
  - a bit of eh)
- stress on the first syllable: KIE-li-ker-ho
vapaaehtoinen: VAH-paa-eh-toy-nen
- va- as in va in van
- paa with a long a (written aa) – hold it a bit longer
- eh as in bet
- toi like toy
- stress again on the first syllable: VA-paa-eh-toi-nen

In Finnish, stress almost always falls on the first syllable of the word.

Is vapaaehtoinen only an adjective, or can it also be a noun?

Vapaaehtoinen can be both:

Adjective – voluntary, optional
- Kielikerho on vapaaehtoinen.
  – The language club is voluntary.
Noun – a volunteer (person)
- Hän on vapaaehtoinen.
  – He/She is a volunteer.

In your sentence it clearly functions as an adjective describing the club.

What’s the difference between vapaaehtoinen and valinnainen?

Both can be translated as optional, but they’re used in different contexts:

vapaaehtoinen – voluntary, something you do of your own free will, not forced
- Kielikerho on vapaaehtoinen.
  – Joining the club is voluntary; no one is required.
valinnainen – elective, optional in a set of choices, especially in schools and courses
- Valinnainen kurssi – an elective course

So a language club where participation is not required is naturally vapaaehtoinen.

How would you say The language clubs are voluntary in Finnish?

Make both the subject and the verb plural, and use the plural predicative form:

Kielikerhot ovat vapaaehtoisia.

Breakdown:

kielikerhot – language clubs (plural nominative: -t ending)
ovat – are (3rd person plural of olla)
vapaahtoisia – plural predicative form of vapaaehtoinen

In the sentence Kielikerho on vapaaehtoinen, which word is the subject and which is the predicative?

Subject: kielikerho – the thing the sentence is about
Verb: on – is
Predicative (complement): vapaaehtoinen – tells what the subject is (what kind of club)

So the sentence structure is:
[Subject] – [to be] – [what the subject is / what kind it is]

Could you expand the sentence to be more explicit, like The language club is a voluntary club in Finnish?

Yes, you can repeat kerho to make it more explicit, although it’s a bit redundant:

Kielikerho on vapaaehtoinen kerho.

This literally says The language club is a voluntary club.
In everyday speech, people would usually just say the shorter:

Kielikerho on vapaaehtoinen.