Kaninen løper gjennom hagen.

Because kaninen is the definite form: the rabbit.

In Norwegian, a noun often gets the meaning of the by adding an ending to the noun itself:

• en kanin = a rabbit
• kaninen = the rabbit

So instead of using a separate word like English the, Norwegian usually adds -en, -a, or -et to the noun, depending on its gender and form.

In Norwegian, the definite article is usually attached to the end of the noun.

So:

• hage = garden
• hagen = the garden

This is one of the biggest differences from English. English says the rabbit, but Norwegian usually says rabbit-the, in effect.

A separate definite word can appear too, but usually when there is an adjective:

• hagen = the garden
• den fine hagen = the nice garden

Løper is the present tense of å løpe = to run.

So:

• å løpe = to run
• løper = run / is running

In Norwegian, the present tense is often formed by adding -r to the infinitive stem:

• å snakke → snakker
• å bo → bor
• å løpe → løper

In many everyday contexts, Norwegian present tense can correspond to both English runs and is running, depending on context.

No. Norwegian verbs do not change for person or number the way English verbs do.

So you get:

• Jeg løper = I run / am running
• Du løper = you run / are running
• Kaninen løper = the rabbit runs / is running
• De løper = they run / are running

This is nice for learners, because you do not need different present-tense forms like English run/runs.

Gjennom usually means through.

In this sentence, it suggests movement from one side of the garden to another, or movement passing within it:

• Kaninen løper gjennom hagen = the rabbit runs through the garden

It is different from:

• i hagen = in the garden
  This only says where the rabbit is.
• over hagen = across/over the garden
  This can suggest crossing it.
• inn i hagen = into the garden
  This focuses on entering it.

So gjennom emphasizes movement through the space.

This is the normal word order for a simple statement in Norwegian:

subject + verb + rest

So here:

• Kaninen = subject
• løper = verb
• gjennom hagen = prepositional phrase

That is very similar to English word order: The rabbit runs through the garden.

If you move another element to the front, Norwegian usually keeps the verb in second position:

• Gjennom hagen løper kaninen.

That sounds more marked or literary, but it is grammatical.

Because the definite ending combines with the noun in a regular Norwegian way.

For many masculine nouns:

• en hage = a garden
• hagen = the garden

You do not simply add -en mechanically to the full indefinite form. The noun changes to its definite form according to standard patterns.

Other examples:

• en bil → bilen
• en katt → katten
• en hage → hagen

So hagen is the correct definite singular form.

Both kanin and hage are commonly treated as masculine nouns:

• en kanin
• en hage

That matters because the common definite singular ending for masculine nouns is -en:

• kaninen
• hagen

In Bokmål, some nouns can vary by dialect or style, and many feminine nouns can also be treated as masculine by many speakers. But for these two nouns, the forms in the sentence are standard and natural.

A learner often notices two tricky sounds here:

• ø in løper
• gj in gjennom

A rough guide:

• løper: the ø is not like a normal English o. It is closer to a rounded vowel made with the tongue somewhat like e but with rounded lips.
• gjennom: in many pronunciations, the beginning sounds something like a soft y sound before the vowel. The g is not pronounced as a hard English g.

Very rough English-friendly approximations are possible, but they are not exact. It is best to hear native audio for these words, especially løper and gjennom, because both contain sounds English does not handle neatly.

Yes, but it means something slightly different.

• Kaninen løper gjennom hagen = the rabbit runs through the garden
• Kaninen løper i hagen = the rabbit runs in the garden

So i hagen tells you the location, while gjennom hagen emphasizes the path or movement through the space.

No. In Norwegian, common nouns are not capitalized just because they are nouns.

Kaninen is capitalized here only because it is the first word in the sentence.

So:

• kaninen
• hagen

would normally be lowercase in the middle of a sentence.

This is different from German, where all nouns are capitalized.