Whose is a relative possessive word. It is used as a determiner before nouns. Whose can refer to both people and things. In its clause whose + noun can be the subject or object of a verb. It can also be the object of a preposition.
- I saw a girl. Her beauty stunned me.
- I saw a girl whose beauty stunned me.
- It was a decision whose importance I did not understand at the moment.
- Today I met John whose mother is an old friend of mine.
Note that whose can be used in both identifying and non-identifying relative clauses.
Of which instead of whose
Instead of whose we can use of which. The most common structure is noun + of which.
- He has acted in a film whose name I can’t remember.
- He has acted in a film the name of which I can’t remember.
- OR He has acted in a film of which I can’t remember the name.
Note that whose is very formal. In an informal style, other structures are often preferred. With, for example, is a common way of expressing possessive ideas.
- I have got a friend whose brother serves in the army. (Formal)
- I have got a friend with a brother who serves in the army. (Informal)