What vs which: the difference, when to use each one and examples

«Excuse me! What’s the difference between what and which?». Aren’t you tired of asking (if you are a student) or being asked (if you are a teacher) this question? I am, for sure. But it is perfectly understandable that many learners have problems with these two words, because they are, in truth, quite similar. And for Spanish speakers it doesn’t help: what is translated as «qué» or «cuál», and which as «cuál» or «qué» depending on the sentence. In other words, both can mean the same, and Spanish gives you no clue.

That is why this post is organised into similarities and differences of use and meaning. I explain when to use each one in questions, in indirect questions and as relative pronouns, give you tables with examples, the most typical mistakes, how it helps you in the Cambridge exams and thirty sentences of exercises with answers. Let’s get started! 🙂

The rule in one sentence: what is open, which is limited

The most important difference, and the one that will help you most, is this:

• Use what when there is no specific set of options: the answer can be almost anything.
• Use which when there is a limited number of options (even if they are three or four, or a group you both already know).

Look at the example:

What would you like in your sandwich? I’ve got cheese or tuna. Which would you prefer?

In the first question we don’t know what is available, so we use what. In the second, the choice is limited to cheese and tuna, so which is compulsory, not what.

What and which in questions

When they work as interrogative pronouns, they can stand alone or go before a noun:

There is a very practical detail: after of we use which, never what: Which of your friends lives in Paris?, not What of your friends…?.

And there are questions that are always asked with what, because there is no list of options: What’s your phone number?, What time is it?, What’s the capital of France?, What do you do on Sundays?

When they are interchangeable

Sometimes both work and the difference is only one of nuance: with what you ask for an opinion without limits, and with which you ask about a group that is already in both people’s minds:

• Which / What would you say is the most beautiful city in the world?
• I’ve no idea which / what road to take to Jimmy’s place.

If you want to review all the question words (who, where, when, why, whose…), have a look at my guide to yes/no and wh- questions in English.

What and which in indirect questions

Both can go at the beginning of a direct question and also of an indirect (embedded) question. The «open» versus «limited» rule is still the same:

• I’m not sure what you mean.
• I don’t know which one to pick.
• Tell me what you want for your birthday.

What and which as relative pronouns

Both also work as relative pronouns, that is, they join two clauses. But here they are not interchangeable:

• Which refers to something you have already named (an antecedent): She went to a conference in Vienna which ended on Friday. / It was a crisis for which he was totally unprepared.
• What means «the thing(s) that» and doesn’t need an antecedent: What they needed was someone to clean their house. / «The Lord of the Rings» is what I am reading at the moment.

The difference, one could say, is that what is less specific than which. This is because what can normally be replaced by the thing which, where «the thing» can be anything. Compare:

• «The Lord of the Rings» is the book which I am reading at the moment. (the book that…)
• «The Lord of the Rings» is what I am reading at the moment. (the thing that…)

That is why I normally tell my students that you cannot use what if you have already specified what you are talking about:

• ✅ Ronda is the Spanish city which Hemingway fell in love with.
• ✅ This is the hammer which was used to kill the victim.

Two more details about which:

• After everything, all, something, nothing and anything we use that (or nothing), not what or which: Everything that he said was true.
• Which can refer to the whole previous clause, separated by a comma: He passed the exam, which surprised everyone.

Common mistakes with what and which

What and which in the Cambridge exams

These two words are very common in the Use of English paper of B2 First and C1 Advanced, especially in Part 2 (open cloze), where you have to fill a gap with one word, and that gap is often a relative pronoun. For example:

• He passed the exam, ______ surprised everyone. → which
• I’m afraid I don’t know ______ to say. → what

Using which to refer to the whole previous clause (…, which surprised everyone) is, in addition, a resource that helps in B2 and C1 Writing to connect ideas naturally.

Summary table

Is «cuál» what or which?

It depends. If the answer is a choice among limited options, which; if there is no group of options, what. For example, «¿cuál es tu número de teléfono?» is What’s your phone number?, and «¿cuál de estos dos prefieres?» is Which of these two do you prefer?.

Is it «what time» or «which time»?

It is what time to ask the time (What time is it?). You would only use which time if you are choosing among specific times: Which time suits you better, five or six?

Can I use «which» to refer to people?

In questions with a choice among people, yes (Which of your teachers do you prefer?). As a relative pronoun for people, use who (or that), not which.

What and which exercises

Thirty sentences to check that you’ve got it. Below you have three interactive exercises that mark themselves, so you will know straight away how you did.

And if you prefer a version in text that you can copy and paste, you have it down here 👇

Exercise 1: what or which?

Choose the correct word to complete each sentence.

Exercise 2: complete the sentences

Write what or which in each gap.

Exercise 3: correct or incorrect?

Decide whether each sentence is correct. If it is incorrect, rewrite it correctly.

Conclusion

To sum up in three ideas: what is for open options and which for limited options; after of, always which; and as relative pronouns they are not interchangeable: what means «the thing that» and which needs an antecedent (or the whole previous clause).

If you like these pairs of words that get confused, have a look at my posts on too and enough, say and tell and win and beat.

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See you in the next post. Until then, don’t forget to keep smiling! 🙂