Learn Hardcore Finnish: Onko lamppu päällä keittiössä?

Onko is on (the 3rd person singular of olla, to be) + the question clitic -ko/-kö, which turns the clause into a yes/no question.
So on → onko = is …? / are …?

What exactly is -ko/-kö, and why is it -ko here (not -kö)?

-ko/-kö is a Finnish enclitic used to form yes/no questions. The choice follows vowel harmony:

Use -ko after back-vowel words (a o u)
Use -kö after front-vowel words (ä ö y)

Because on contains o (a back vowel), you get on + ko → onko.

Is Onko lamppu… the only possible word order for this question?

No. This is a very neutral, common order, but Finnish word order can shift for emphasis or focus. For example:

Onko lamppu päällä keittiössä? (neutral)
Onko lamppu keittiössä päällä? (can slightly highlight where)
Lamppuko on päällä keittiössä? (emphasizes the lamp specifically: “Is it the lamp that’s on…?”)
Keittiössäkö lamppu on päällä? (emphasizes in the kitchen)

The basic meaning stays similar; the focus changes.

Why is lamppu in this form? Should it have an ending?

Lamppu is the subject and is in the nominative singular (the dictionary form). In a simple “X is Y” type sentence, the subject is typically nominative:

Lamppu on päällä. (The lamp is on.)

No extra case ending is needed here.

What does päällä literally mean, and why is it used for a lamp being on?

Literally, päällä is the adessive form of pää (head) and originally relates to being on top / on something. In modern Finnish, olla päällä is an established idiom meaning to be on / switched on / running, especially for:

lights: lamppu on päällä
devices: tietokone on päällä
systems: lämmitys on päällä

So it’s a standard way to say something is “on” in the powered/active sense.

Is päällä a postposition here (like “on top of”), or something else?

Here päällä functions as a predicative adverbial in the fixed expression olla päällä (“to be on”).
It’s not taking a noun complement the way it would in a more literal “on top of X” sense.

Compare:

Device-state: Lamppu on päällä. (The lamp is on.)
Location/top-of sense: Kirja on pöydän päällä. (The book is on the table.)
Here pöydän is genitive, and päällä behaves more like a postposition (“on top of”).

Why is keittiössä in that form, and what does the ending mean?

Keittiössä is keittiö (kitchen) + -ssä, the inessive case, meaning in (inside):

keittiö → keittiössä = in the kitchen

Finnish often uses cases instead of separate prepositions like “in/at/from”.

Could you also say keittiöllä instead of keittiössä?

Sometimes, but it changes the nuance.

keittiössä (inessive) = inside/in the kitchen (most typical here)
keittiöllä (adessive) can mean at/by the kitchen (more like being in the vicinity, or at a location associated with it)

For a lamp being on in the room, keittiössä is the natural choice.

Does Finnish need a word for the (like “the kitchen”, “the lamp”)?

No. Finnish has no articles (a/an/the). Context supplies definiteness:

lamppu can mean a lamp or the lamp
keittiössä can mean in a kitchen or in the kitchen

If you really need to specify, Finnish uses other tools (demonstratives like se “that/the”, or context-specific phrasing), but there’s no direct article system.

How would you answer this question briefly in Finnish?

Common short answers are:

On. = Yes (it is).
Ei ole. (or Ei.) = No (it isn’t).

You can also be more specific:

On, se on päällä. = Yes, it’s on.
Ei, se ei ole päällä. = No, it’s not on.

What’s the negative version of the whole sentence?

A straightforward negative statement would be:

Lamppu ei ole päällä keittiössä. = The lamp isn’t on in the kitchen.

A negative question (“Isn’t the lamp on…?”) could be:

Eikö lamppu ole päällä keittiössä?