16.3.3 declension
of sein and ihr (3rd person singular)
For the 3rd person singular,
there are two different possessive pronouns, as in English
as well. As you can see the logic is the same. The possessive
pronoun is determined by the owner of the object. The
gender and number of the declension is determined by
the object owned. The declension is determined by the
relation between the objects or the subject and the object.