"I need my book."

Translation: Jag behöver min bok.

[HoroTanuki]

why can't this be "Jag behöver sin bok"? (if "sin" means "my own")

[devalanteriel]

You're on the right track, but sin is used for third person, min for first person singular. So sin means "his/her/its own", not "my own".

Here's a full list of reflexive possessive pronouns (common gender):

• jag - min
• du - din
• han/hon/den/det - sin
• vi - vår
• ni - er
• de - sin

[HoroTanuki]

Oh, thanks, I was comparing it to my language (moj/svoj (my/my own)) and since "svoj" starts with an "s" the same as "sin" I thought min and sin are interchangeable. My bad :)

[Ulincsys]

I have been looking for a comparison chart on pronouns like this for a while, have a Lingot!