Which vs. What

There is little difference of meaning between which and what.

• Which/what is the largest continent in the world?
• Which/what train did you come on?

Which is preferred when the speaker has a limited number of choices in mind.

• We have got white and brown bread. Which will you have?
• Which colour do you want – red, pink, blue or purple?

When the speaker is not thinking of a limited number of choices, what is used.

• What is your telephone number? (NOT Which is your phone number?)
• What language do they speak in Chile? (More natural than Which language …)

Before nouns, which and what can be used to ask questions about both people and things.

• Which teacher do you like best?
• What writers do you like?
• Which colour do you want – red or brown?

When these words are used as pronouns, without nouns immediately after them, we use who, not which, for people.

• Who is your favourite writer? (NOT Which is your favourite writer?)
• Who won – Alan or Peter? (NOT Which won …)

However, which can be used in questions about people’s identity, and what can be used to ask about people’s jobs and functions.

• ‘Which is your boy?’ ‘The one blue shirt.’
• ‘What is your husband?’ ‘He is a doctor.’