Difference between ‘what’ and ‘which’?

Difference between ‘what’ and ‘which’

Learners of English often are confused between the use of ‘what’ and ‘which’ in a sentence. Look at these two sentences:

1. What is your name?
2. Which is your name?

Though both the sentences are grammatically correct, we always use the first sentence that starts with ‘what’. The reason is ‘what’ refers to an open set and ‘which’ refers to a closed set. In the first sentence (What is …), the speaker has no chance of guessing any name. In the second sentence (Which is…), the speaker may have a few names in mind or on the list. "Which" generally suggests there are two or more possibilities and the person asking "which" probably knows what they are. Here are a few more examples:

‘What’ refers to an open set: What is your mother tongue? It could be any language and the person asking the question does not know what it is.

• What is the name of the examiner?
• What are the different options?

‘Which’ refers to a closed set: In which city were you born?’ It could be any of the cities which the person who asks the question knows.

• Which (of these) stories have you read?
• Which (of the) countries have you visited?

In the above sentences, it is not possible to replace ‘which’ with ‘what’. If the choice is clearly restricted, then 'which' is the better choice.

Both “what” and “which” are interrogative as well as relative pronouns.
As an interrogative pronoun, ‘what’ in a question suggests unlimited possibilities. Here are a few examples:

• What are you going to do this weekend?
The answer could be almost anything.
• What is your favorite picnic spot.
The answer could be any picnic spot.

“Which” in a question suggests a definite, limited list of alternatives. Look at these examples:
• Which game do you like the most?
Both the speaker and the listener have a few games in mind.

As a relative pronoun, ‘what’ means unlimited possibilities. Examples:
• The examiner asked the student what his name was.
• We don’t know what we are going to do this weekend.

“Which’ as a relative pronoun is specific. Examples:
• I went to Goa which is a beautiful place.
• I want to present a laptop to my boyfriend, but I don’t know which one to buy.

‘What’ is used in a range of expressions, all giving the idea of ‘no limits’. Examples:

• What about …
• What if …