We use interrogative pronouns to ask questions. They are: who, which, whom, what and whose. These are also known as wh-words. Questions using these are called wh-questions:
Who called last night?
Which keys are yours?
Whom do I ask for at the desk?
What did you do when the electricity failed?
Whose watch is this?
Interrogative pronouns: uses
We use who and whom on their own:
Whom did you speak to?
We can use whose, which and what either on their own (as pronouns) or with a noun head (underlined):
With a noun head
We can use who, whose, which and what both as subject and object:
Who is the best footballer in the world? (who as subject)
Who did you meet? (who as object)
What happened next? (what as subject)
What did you buy? (what as object)
Who or whom?
We use whom as an object in formal styles. When we use a preposition before whom, it is even more formal. We don’t normally use it in speaking:
Whom did you give the book to? (formal)
To whom did you give the book? (very formal) Or, less formally: Who did you give the book to?
What or which?
We use what when we ask about specific information from a general range of possible answers:
What’s the tallest building in the world?
What did you say? I couldn’t hear you.
What’s your address?
We use which when we ask for specific information from a restricted range of possible answers:
[looking at a list of addresses]
Which is your address?B:
This one here.
Which hand do you write with?
[looking at a photograph of three women]
Which one is your sister?
Which airport do we leave from, Heathrow or Gatwick?