Käytävän valo valaisee portaikon.

The light of the corridor illuminates the staircase.

Breakdown of Käytävän valo valaisee portaikon.

• valo: the light
• portaikko: the staircase
• käytävä: the corridor
• valaista: to light

Questions & Answers about Käytävän valo valaisee portaikon.

What case is käytävän, and what does it express in this sentence?

Käytävän is in the genitive singular case of käytävä (corridor, hallway).

• käytävä → käytävän (genitive)
• The genitive often corresponds to English "of X" or "X's".

So käytävän valo literally means "the corridor’s light" or "the light of the corridor".
The genitive here is used to show that the light belongs to or is associated with the corridor.

Why is it käytävän valo and not käytävä valo?

Finnish normally uses the genitive + noun pattern to express possession or association:

• käytävän valo = the corridor’s light / the light of the corridor

If you said käytävä valo without the genitive, käytävä would be understood as an adjective-like word modifying valo, roughly "walkable light" or "corridor-type light", which is not how Finns naturally say "the corridor light".

So käytävän valo is the standard, natural way to say "the corridor light".

What exactly is the subject in this sentence?

The full subject is the noun phrase käytävän valo.

• käytävän (genitive attribute: of the corridor)
• valo (head noun: light)

So grammatically, valo is the head of the subject, and käytävän specifies which light. Together, käytävän valo is "the one that does the illuminating," i.e., the subject of valaisee.

What form is portaikon, and why does it end in -n?

Portaikon is also genitive singular of portaikko (stairway, stairwell):

• portaikko → portaikon (genitive)

In this sentence, that genitive form is functioning as a total object of the verb valaisee.

For ordinary nouns, the genitive singular (-n) is often the form used for a complete/total object (the whole stairway is being lit, not just part of it). So:

• valaisee portaikon ≈ "illuminates the (whole) stairway"

So is portaikon a genitive or an accusative object?

Formally, portaikon is in the genitive singular form.

In traditional teaching, you often see:

• Genitive object = total object in many contexts (like here)

So teachers often just say "genitive object" rather than going deeply into the accusative terminology. For practical purposes as a learner:

• Treat portaikon here as a total object marked with -n, showing that the stairway is seen as a complete thing being illuminated.

Could I say Käytävän valo valaisee portaikkoa instead? What would change?

Yes, portaikkoa is possible, but the nuance changes.

• portaikon (genitive / total object): the stairway is viewed as a whole; the event is bounded/complete – "illuminates the stairway (as a whole)."
• portaikkoa (partitive / partial object): the action is unbounded, ongoing, or affects only part of the stairway.

In many everyday contexts, speakers still prefer portaikon here, because "lighting the stairway" is naturally understood as affecting the whole thing. Portaikkoa could sound more like focusing on the process of illuminating, or on lighting some part of it.

Can I change the word order to Portaikon valaisee käytävän valo? Does it still mean the same?

Yes, Finnish word order is quite flexible, and Portaikon valaisee käytävän valo is grammatically correct.

• Käytävän valo valaisee portaikon.
  • Neutral word order: subject (käytävän valo) first, object (portaikon) after the verb.
• Portaikon valaisee käytävän valo.
  • Emphasizes portaikon (the stairway), often used when contrasting or answering a "what is being lit?"-type question.

The basic meaning ("The corridor light illuminates the stairway") is the same, but the focus and emphasis shift.

There’s no word for “the” here. How do we know it means “the corridor light” and “the stairway”, not “a”?

Finnish has no articles (no direct equivalents of a/an/the).

Definiteness and indefiniteness are usually understood from:

• Context (things already known or mentioned)
• Specificity (is it a particular corridor/light we both know?)
• Real‑world plausibility (a building usually has one specific corridor light in mind)

So käytävän valo valaisee portaikon can be translated as:

• "The corridor light illuminates the stairway"
  or
• "A corridor light illuminates a stairway"

The choice of the vs a is something English has to add; Finnish leaves it to context.

What is the difference between portaikko and portaat?

Both relate to stairs, but they’re used a bit differently:

• portaikko
  • the stairway / staircase as a structure or space
  • often includes the idea of the stairwell area
• portaat
  • literally "steps", usually the individual steps or the whole flight of steps

In this sentence, portaikon works well because we’re talking about lighting the stairway area (not just individual steps).
You could sometimes also hear Käytävän valo valaisee portaat, but it slightly shifts the focus more onto the steps themselves.

What does the verb valaisee tell us about person, number, and tense?

Valaisee is:

• 3rd person singular
• Present tense
• Indicative mood
• From the verb valaista (to illuminate, to light up)

So it corresponds to English "illuminates" / "lights (up)", with the subject being he/she/it or some singular noun phrase (here: käytävän valo).