Min søster har seks bøger i sin taske.

Because Danish possessives change according to the noun being possessed.

Here, søster is a common-gender singular noun, so you use min:

• min søster
• mit hus for a neuter singular noun
• mine bøger for a plural noun

So the form depends on the noun after the possessive, not on the speaker.

When Danish uses a possessive like min, it normally does not use an article like en or den with the noun.

So you say:

• min søster
• not min en søster

This works much like English: we say my sister, not my a sister.

No. In Danish, the present tense verb is the same for all persons.

So you get:

• jeg har
• du har
• han har
• vi har

Unlike English, Danish does not add a special -s form for he/she/it in the present tense.

After a number, Danish normally uses the plural indefinite form of the noun, with no article.

So:

• seks bøger
• to biler
• tre huse

This is similar to English: six books, not six the books.

Yes, it is somewhat irregular.

The forms are:

• en bog — singular indefinite
• bogen — singular definite
• bøger — plural indefinite
• bøgerne — plural definite

The vowel changes from o to ø, and the plural ending is -er. So this is not a completely regular pattern you could predict just from the singular form.

Because sin is the reflexive possessive. It is used when the owner is the same as the subject of the clause.

In this sentence, the subject is min søster, and the bag belongs to my sister, so Danish uses sin:

• Min søster har seks bøger i sin taske.

If you said hendes taske, it would usually suggest the bag belongs to some other female person, not the sister who is the subject.

This is one of the most important differences between Danish and English, because English uses her in both situations.

Because sin/sit/sine must agree with the noun that follows.

• sin
  • common-gender singular noun
    
    • sin taske
• sit
  • neuter singular noun
    
    • sit hus
• sine
  • plural noun
    
    • sine bøger

Since taske is a common-gender singular noun, sin is the correct form.

After a possessive, Danish normally uses the indefinite form of the noun, even though the meaning is definite.

So you say:

• min taske
• sin taske
• hendes taske

Not:

• min tasken
• sin tasken

This is different from English in form, but the meaning is still definite: her bag / his bag / my bag.

The sentence uses normal Danish main-clause word order:

• Min søster = subject
• har = finite verb
• seks bøger = object
• i sin taske = adverbial phrase

So the basic order is:

Subject + verb + other elements

Danish is a V2 language, which means the finite verb usually comes in the second position in main clauses. If you move another element to the front, the verb still stays second:

• I sin taske har min søster seks bøger.

That version is grammatical, but the original sentence is the most neutral and natural.

Here i means in or inside.

So i sin taske means in her own bag.

Danish i is very common and often matches English in, though in other contexts prepositions do not always line up perfectly between the two languages.

The letter ø is a special Danish vowel, and it does not have a perfect English equivalent.

A rough guide:

• It is a rounded front vowel
• Your tongue is somewhat like for eh/ih
• But your lips are rounded, almost like for oo

For learners:

• søster is roughly something like SUH-ster with rounded lips, but not exactly
• bøger has the same vowel quality in the first syllable

It is worth practicing ø separately, because it is very common in Danish and changing it can make the word sound wrong or become a different word.

Grammatically, that is possible, but it usually changes the meaning.

• i sin taske = in her own bag, where her refers back to my sister
• i hendes taske = in her bag, but usually referring to another woman/girl

So in this sentence, if the bag belongs to the sister, sin is the natural and correct choice.