Learn Hardcore Finnish: Portaikko on joskus liukas, joten omistaja lisää varoituskyltin. - The staircase is sometimes slippery, so the owner is adding a warning sign.

Portaikko means “staircase.” In the sentence it is the subject of the copular verb on (“is”), so it stays in the nominative case. Subjects of olla (“to be”) always take the nominative.

Why is the adjective liukas not in the partitive form (liukasta)?

Because liukas (“slippery”) is a predicate adjective linked by on. Predicate adjectives after olla are always in the nominative to agree with the subject (portaikko).

What role does joskus play, and can it move around in the sentence?

Josskus means “sometimes.” It’s an adverb modifying on liukas (“is slippery”). Finnish adverbs are fairly free in word order, so you could say Portaikko on liukas joskus, Joskus portaikko on liukas or Portaikko joskus on liukas, though the original sounds most natural.

What is joten, and how is it used here?

Joten is a coordinating conjunction meaning “so” or “therefore.” It links two clauses to show cause and effect: “The staircase is sometimes slippery, so the owner adds a warning sign.”

The verb lisää – which verb form is this, and what does it mean?

Here lisää is the present tense, third person singular of lisätä (“to add”). It means “(he/she/it) adds.”

Why is varoituskyltin in the accusative/genitive form, not the partitive?

Because lisätä is a transitive verb taking a complete (countable) object. In the present tense, a fully affected singular object uses the accusative, which in Finnish looks identical to the genitive (–n ending). If it were an indefinite amount or an ongoing action, you’d use the partitive (varoituskylttiä), but here the owner adds exactly one sign.

How is the compound varoituskyltti formed?

It combines varoitus (“warning,” noun) + kyltti (“sign”). You simply attach the words: varoitus + kyltti → varoituskyltti. The final –ti of kyltti stays intact, and when you add the accusative –n you get varoituskylttin.

Can you explain the difference between accusative and partitive objects in Finnish verbs?

Accusative (identical to the genitive for singular nouns): used for a complete, countable object in perfective actions (e.g. “I ate the cookie” → Söin keksin).
Partitive: used for partial, indefinite, or ongoing actions (e.g. “I’m eating cookies” → Syön keksejä).

Why isn’t there an article like “the” or “a” before omistaja?

Finnish has no articles. Definiteness or indefiniteness is inferred from context. Here omistaja can mean “the owner” or simply “an owner,” but in English translation you supply “the” because the context implies a specific owner responsible for the staircase.

Could you replace joten with niin että here?

Yes, you could say Portaikko on joskus liukas, niin että omistaja lisää varoituskyltin, but it shifts the nuance slightly. Niin että (“so that”) often emphasizes purpose or result more explicitly, whereas joten is a straightforward “so.” Both are correct, though joten is more concise in this case.