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What vs. Which

Hello! This week on Ask a Teacher, we will answer a question from Zehra, a reader of our website, about the difference between using the question words "what" and "which."

Question:

Hello,

Could you please tell me which one is correct? "What color is missing¹?" or "Which color is missing?"

Zehra

Answer:

Dear Zehra,

Thank you for your question! Either of these questions could be correct.

"What" and "which" can both be used to form a question. So, either of these questions could be correct. It depends on the situation and the information we are seeking. Let us consider each question word more closely².

What

When we ask a question using "what," we are asking for information because we do not know the answer. The information can be about things or actions.

For example:

What is your favorite kind of pizza?

In this example, the person who asks the question does not know what kind of pizza the other person likes.

There can be an unlimited³ number of possible answers. This is important when trying to decide between the two question words.

A person answering the pizza question could say a favorite combination⁴ of toppings, like meat and cheese, or even a favorite style of pizza.

Which

We use "which" to ask questions about specific information or when we are presenting a set of choices.

We may have some background information that we want to explore more by using a "which" question.

For example, if I am in a parking lot with my friend and I know she has a car but am unsure which is hers, I could ask a question using "which."

Which is yours, the blue truck or the red car?

Here, the question deals with a limited choice. So we use the question word "which."

Summary

We can use an example using geography to easily show the difference between "what" and "which."

What is the capital of the United States?

The answer is unknown, and the choices are unlimited.

Which is the capital of the United States: Philadelphia or Washington, D.C.?

There are only two choices.

Using "what" suggest that the questioner does not know the answer and that there is no limit to the number of possible answers.

If you choose "which" as your question word, you may have prior⁵ knowledge and you are asking for information that is more specific. You may also be limiting the decision to a few choices.

Please let us know if these examples and explanations have helped you, Zehra!

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Words in This Story

toppings – n. ingredients⁶ that are placed on top of a main dish, like on pizza or ice cream

style –n. a particular way of doing, preparing or designing something

prior – adj. existing earlier in time