Learn Hardcore Norwegian: Sønnen hennes løper opp trappen og rutsjer ned sklien igjen og igjen. - Her son runs up the stairs and slides down the slide again and again.

Sønnen hennes = the son of hers
- Possessive comes after the noun.
- The noun is in definite form (sønnen = the son).
- This is the most neutral, everyday way to say her son in Norwegian.
hennes sønn = her son (with emphasis on her)
- Possessive comes before the noun.
- The noun is usually in indefinite form (sønn).
- This often adds emphasis or contrast:
  - Det er hennes sønn, ikke min. – That’s her son, not mine.

In your sentence, Sønnen hennes løper … is the natural, neutral way to refer to her son that the listener already knows about from context.

Why can Norwegian use sønnen hennes (definite) when English just says “her son” (indefinite)?

Norwegian often uses a “double definiteness” pattern when the possessive comes after the noun:

sønnen hennes
- sønnen = the son (definite)
- hennes = her

Literally, this is close to “the son of hers”.
English normally doesn’t mark definiteness on the noun in this construction, so it just says her son.

This pattern is very common:

boka mi – my book (literally the book my)
foreldrene hans – his parents (literally the parents his)

So Sønnen hennes is perfectly normal and does not feel “too definite” to a Norwegian speaker.

Why is it hennes and not sin in Sønnen hennes?

Sin / si / sitt / sine are reflexive possessives. They refer back to the subject of the same clause.

In your sentence, the subject is Sønnen hennes (her son). If you wrote sønnen sin, sin would refer back to sønnen:

Sønnen sin løper …
≈ His own son runs … (the son has a son – weird meaning here)

But we want to say her son (the mother’s son), and the mother is not the subject of this sentence, so we must use:

hennes for her (belongs to some woman who is not the subject)
similarly: hans for his (non‑subject male possessor)

So:

Sønnen hennes løper … – Her son runs …
Han ser sønnen sin. – He sees his (own) son.
Hun ser sønnen hans. – She sees his son (someone else’s).

In your sentence only hennes is correct.

What is the grammatical form of Sønnen and what is the base word?

Base word: en sønn – a son (masculine noun)

Forms you see here:

sønnen – the son (definite singular: -en)
sønn – son (indefinite singular)
sønner – sons (indefinite plural)
sønnene – the sons (definite plural)

So Sønnen hennes literally means the son of hers.

Why is it trappen and not just trapp?

Because it refers to a specific staircase, so Norwegian uses the definite form:

en trapp – a stair / staircase
trappen – the stairs / the staircase

In the sentence, he is running up the stairs that are present in the situation, so Norwegian marks this with -en:

løper opp trappen – runs up the stairs

You could also see trappa instead of trappen; more on that below.

What’s the difference between trappen and trappa?

The base noun is feminine:

en trapp – a stair, a staircase

In Bokmål, feminine nouns often have two possible definite forms:

trappen – grammatically correct, somewhat more formal/neutral
trappa – also correct in Bokmål; often more colloquial, very common in speech

So both are fine:

løper opp trappen
løper opp trappa

Meaning is the same; it’s mostly a style/variety choice.

What is sklien and what is its base form?

Base word: en sklie – a slide (like in a playground)

Main forms:

en sklie – a slide (indefinite singular)
sklien – the slide (definite singular)
sklier – slides (indefinite plural)
skliene – the slides (definite plural)

So ned sklien = down the slide (a particular, known slide).

Why is it opp trappen and ned sklien? Could I say trappen opp or sklien ned?

opp and ned here are directional adverbs/particles meaning up and down.

The standard way to express movement along something is:

verb + opp + noun (definite)
løper opp trappen – runs up (along) the stairs
verb + ned + noun (definite)
rutsjer ned sklien – slides down (along) the slide

You can say trappen opp or sklien ned, but this usually changes the meaning or sounds less natural:

løper trappen opp – possible, but more marked; can sound more literary or give slightly different rhythm/emphasis.
sklien ned also sounds odd; in practice people say ned sklien.

For a learner, it’s safest to stick to:

løpe opp trappen, gå ned bakken, klatre opp stigen

What’s the infinitive of rutsjer, and is it the usual word for “to slide” on a slide?

Infinitive: å rutsje – to slide (down something)
rutsjer is the present tense: slides / is sliding.

Yes, this is a very normal verb to use for kids sliding on a slide:

Barna rutsjer ned sklien. – The children slide down the slide.

There are other verbs:

å skli – to slip, slide (more general, like slipping on ice)
å ake – to sled, to ride a sledge/toboggan

For a playground slide, å rutsje is very natural.

What does igjen og igjen add, and how is it different from just igjen?

igjen alone = again (one more time):
- Han gjør det igjen. – He does it again (once more).
igjen og igjen = again and again, over and over
It emphasizes repetition, many times:
- Sønnen hennes løper opp trappen og rutsjer ned sklien igjen og igjen.
  → He keeps doing this many times.

Other ways to express repetition:

om igjen og om igjen – very similar to igjen og igjen
hele tiden – all the time, constantly
på nytt – again, anew (more neutral, often just once)

Why is there no comma before og in …løper opp trappen og rutsjer ned sklien…?

In Norwegian, you do not normally put a comma between two verbs that share the same subject in a simple clause.

Here:

Subject: Sønnen hennes
Verb 1: løper
Verb 2: rutsjer
Connector: og

So it stays:

Sønnen hennes løper opp trappen og rutsjer ned sklien …

You would add a comma before og if you’re connecting two full main clauses, each with its own subject:

Sønnen hennes løper opp trappen, og vennene hans roper etter ham.
(clause 1: Sønnen hennes løper … / clause 2: vennene hans roper …)

Why does Norwegian use simple present løper / rutsjer instead of a continuous form like English “is running / is sliding”?

Norwegian does not have a grammatical present continuous tense like English. The simple present covers both:

Sønnen hennes løper opp trappen.
= Her son runs up the stairs.
or
= Her son is running up the stairs. (in the right context)

If you really want to emphasize that something is happening right now, you can use holder på å + infinitive, but that’s more marked:

Han holder på å løpe opp trappen. – He is (currently) running up the stairs.

In your sentence, normal present løper / rutsjer is the natural way to express an ongoing repeated activity.

What is the difference between opp and oppe, and between ned and nede?

opp and ned → movement / direction (upwards, downwards)
oppe and nede → location / state (up, down)

Compare:

Han løper opp trappen. – He runs up the stairs. (movement)
Han er oppe. – He is upstairs / up. (location)
Han rutsjer ned sklien. – He slides down the slide. (movement)
Han er nede. – He is downstairs / down there. (location)

Your sentence describes movement, so opp and ned are correct.

Any pronunciation tips for løper, rutsjer, sklien, and igjen for an English speaker?

Approximate pronunciation (Standard Eastern Norwegian, IPA in slashes):

løper – /ˈløːpər/
- lø- like French bleu or German schön (rounded ø sound)
- long ø: løø-per
rutsjer – /ˈrʉtʂər/
- ru: rounded front vowel ʉ (like Swedish u or in Oslo accent u).
- tsj is one sound, like English “ch” but a bit more retroflex.
- Roughly: “RUHT-sher”, with a Norwegian u.
sklien – /ˈskliːən/ (often [ˈskliːn])
- skl cluster is pronounced together: skl‑ as in skl- one syllable.
- ie gives a long i sound: sklii-en.
igjen – /iˈjɛn/ or /ˈjɛn/ (in fast speech often just jenn)
- Start with a short i (like bit but closer), then jen: i-YEN.

Listening to native audio and repeating these words in short phrases (e.g. opp trappen, ned sklien, igjen og igjen) will help you internalize the rhythm and sounds.