Questions & Answers about Pappan läser sin bok i huset.
Why does the sentence use sin instead of hans for "his"?
In Swedish, you must use sin (or sitt/sina) when a third-person subject is doing something to their own thing. Here, the father is the subject, and he is reading his own book. If the sentence said Pappan läser hans bok, it would mean he is reading another man's book!
Why is it sin here, rather than sitt or sina?
The reflexive possessive pronoun changes to match the noun being owned, not the owner. Because bok is a singular en-word (en bok), we use the en-word form sin. If he were reading a letter (ett brev), it would be sitt brev, and if he were reading multiple books, it would be sina böcker.
We know it's a specific book he is reading. Why is it bok and not the definite form boken?
In Swedish, you never use the definite form of a noun right after a possessive pronoun. Just like in English you wouldn't say "his the book", in Swedish you must use the indefinite form: sin bok.
Since "a father" is en pappa, shouldn't "the father" be pappaen?
For en-words, you usually add -en to the end to make them definite. However, when a word already ends in a vowel (like pappa), you just add -n so it is easier to pronounce. That is why en pappa becomes pappan.