Learn Hardcore Finnish: Illalla suljen oven ja sammutan valon. - In the evening I close the door and turn off the light.

The ending -lla is the adessive case, which often expresses location or time.
Literally it’s something like “on the evening”, but idiomatically it means “in the evening / this evening / tonight” (context decides how specific it is).

Other common time expressions with the same pattern:

aamulla – in the morning
päivällä – in the daytime / during the day
yöllä – at night

Why does the sentence start with Illalla? Could I say Suljen oven illalla instead?

Both are correct Finnish:

Illalla suljen oven ja sammutan valon.
Suljen oven illalla ja sammutan valon.

Putting Illalla first is a very natural way to set the time frame: “In the evening, I close the door and turn off the light.”

Word order in Finnish is flexible, but:

Time expressions (Illalla, Huomenna, etc.) often come at the beginning when you want to emphasize when something happens.
Suljen oven illalla is also fine; it just sounds slightly more neutral/focus-on-the-action than focus-on-the-time.

Why is suljen present tense when the English translation is “I will close”?

Finnish does not have a separate future tense. The present tense often covers both:

now / regularly and
future, when there is a future time word in the sentence.

Examples:

Illalla suljen oven. – This evening I will close the door.
Huomenna menen kouluun. – Tomorrow I will go to school.
Joka ilta suljen oven. – Every evening I close the door. (habitual)

So context (words like illalla, huomenna, ensi viikolla) gives the future meaning.

Where is the subject “I”? Why is minä missing?

The subject is included in the verb ending.

suljen = I close
sammutan = I turn off / extinguish

The -n ending on the verb marks 1st person singular (I). Because of this, you normally omit the pronoun:

Illalla suljen oven ja sammutan valon.
= In the evening I (will) close the door and (I) (will) turn off the light.

You can include minä for emphasis or contrast:

Illalla minä suljen oven. – In the evening *I (as opposed to someone else) close the door.*

But repeating minä before every verb (minä suljen… ja minä sammutan…) sounds heavy or childlike in neutral speech.

Why is it oven and not ovi? What case is oven?

Oven is the genitive singular of ovi (door).

Declension:

nominative: ovi – the base form (door)
genitive: oven – of the door / the door (as object)
partitive: ovea – some of the door / the door (incomplete)

In suljen oven, oven is a total object:

You close the whole door, and the action is seen as reaching its end point (it ends up closed).
Total objects of this type usually use the genitive form, which looks like oven.

Compare:

Suljen oven. – I (will) close the door (completely).
En sulje ovea. – I’m not closing the door. (negative → partitive ovea)

For now, it’s enough to remember:
→ After verbs like sulkea with a complete, positive action, the object is often in the genitive: oven.

Why is it valon and not valo or valoa?

Valon is the genitive singular of valo (light):

nominative: valo – light (subject form)
genitive: valon – of the light / the light (as total object)
partitive: valoa – some light / light (unbounded)

In sammutan valon:

The action is complete: you turn the light fully off.
That’s why the light is a total object, shown by the genitive form valon.

Compare:

Sammutan valon. – I (will) turn off the light. (light goes from on → off)
Sammutan valoja. – I’m turning off some lights. (partitive plural, unbounded amount)
On paljon valoa. – There is a lot of light. (partitive for uncountable / “some amount of”)

How do we get suljen from the infinitive sulkea (“to close”)?

Verb: sulkea – to close, to shut.

Present tense, singular:

minä suljen – I close
sinä suljet – you close
hän sulkee – he/she closes

The patterns:

The stem is sulke-.
For minä, Finnish adds -n to the stem.
In speech and writing, k between vowels often weakens to j here, giving suljen (not sulken).

So you get:

sulke- + n → suljen

You don’t have to fully understand the historical sound change; just learn the forms:

minä suljen
sinä suljet
hän sulkee

What’s the difference between sammutan and sammun?

These come from two different but related verbs:

sammuttaa – to extinguish, to put out, to turn off (something)
- transitive (you do it to something)
- minä sammutan valon. – I turn off the light.
sammua – to go out, to be extinguished, to turn off by itself
- intransitive (no direct object)
- Valo sammuu. – The light goes out.

So:

sammutan = I turn something off.
sammun = I go out / go off (or “I pass out” in some contexts).

In the sentence Illalla suljen oven ja sammutan valon, you must use sammutan, because you are actively turning the light off.

Is ja used just like English “and” here? Can I replace it with a comma?

Yes, ja means “and” and is used very much like in English:

suljen oven ja sammutan valon
= I (will) close the door and turn off the light.

You cannot replace ja with just a comma in Finnish.
You need to explicitly use ja between two independent verb phrases:

✔ Illalla suljen oven ja sammutan valon.
✖ Illalla suljen oven, sammutan valon. (grammatically odd / incomplete)

A comma alone between two finite verbs, without ja, is generally not correct Finnish.

How would I say “In the evenings I usually close the door and turn off the light,” not just tonight?

To express a habitual action (in the evenings, generally), you typically use iltaisin instead of illalla:

Iltaisin suljen oven ja sammutan valon.
= In the evenings I (usually) close the door and turn off the light.

Contrast:

Illalla suljen oven… – This (or that) specific evening / tonight.
Iltaisin suljen oven… – On evenings in general, as a habit.

Why is there no word for “the” before oven and valon?

Finnish has no articles (no words for “a/an” or “the”).

ovi can mean a door or the door, depending on context.
oven can mean a/the door’s or the door as an object, again depending on context.

So:

Illalla suljen oven ja sammutan valon.
can be translated naturally as
→ In the evening I (will) close *the door and turn off the light.*

The idea of definiteness (“the”) is expressed by context, not by a specific article word.