Which and what
There is little difference of meaning between which and what. They are often both possible.
- Which is your favorite song? OR What is your favorite song?
- Which writer / what writer has influenced you most in your life?
We prefer which when the number of choices is limited.
- We have got small or large eggs. Which will you have? (More natural than ‘What will you have?’)
What is preferred when the number of choices is unlimited.
- What is your phone number? (More natural than ‘Which is your phone number?’)
- What is your name? (NOT Which is your name?)
What and which are usually used to ask about things.
- What would you like for breakfast?
- Do what you think is right.
Before nouns, which and what can be used to ask questions about both things and people.
- What books have you read on this subject?
- What time is it?
- What authors do you like best?
- Which teacher do you like best?
- Which way shall we go?
- Tell me which books on my shelf you would like to borrow.
Before a noun with a determiner (e.g. the, my, this etc.), we use which of. Who and what are not normally used with of.
- Which of your teachers do you like best? (NOT Who of / what of your teachers do you like best?)
Who, what and which as pronouns
When these words are used as pronouns, without nouns immediately after them, we generally use who for people.
- Who won – John or Peter? (NOT Which won – John or Peter?)
- Who is she going out with?
Which can be used in questions about people’s identity and what can be used in questions about people’s jobs and functions.
- ‘Which is your boy?’ ‘The one in blue shirt.’
- ‘What is your husband?’ ‘He is a doctor.’