What, that and which
What means "the thing that": what I need is rest. After all, everything or something, use that, not what: all I need.
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What contains its own noun: it means "the thing that" or "the things that". That and which need a noun or pronoun before them to refer to. So after a noun, and after words like all, everything, something and nothing, use that (or nothing), not what.
Word | What comes before it | Example |
|---|---|---|
what | no noun | What I need is a holiday. |
that | a noun, all, everything | All (that) I need is a holiday. |
which | a noun, or a whole clause | It rained, which was a pity. |
What = the thing that
A what clause works like a noun. It can be the subject or the object of the sentence, or follow a preposition.
- What she said made me angry.
(The thing that she said made me angry.)
- I didn't understand what he wanted.
- Show me what you bought.
- We talked about what happened at the meeting.
Not what after a noun
You met this at B1. After a noun, the relative word is that, which or who, or nothing.
- Incorrect: The film what we saw last night was too long.
- Correct: The film (that) we saw last night was too long.The noun film is already there, so use that or which, not what.
After all, everything, something, nothing: that
All, everything, something, anything, nothing and the only thing already do the job of the noun. After them, use that, or leave it out when it is the object.
- All (that) I need is a good night's sleep.
- Everything (that) she said was true.
- There's something (that) I want to tell you.
- Nothing that he did surprised me.
- The only thing that matters is that you're safe.
- Incorrect: All what I need is a few days off.
- Correct: All (that) I need is a few days off.All already means "the thing". Use that or nothing after it, never what.
- Incorrect: Everything what he told me was a lie.
- Correct: Everything (that) he told me was a lie.
After something, nothing, everything and the only thing, which is possible but much less common. After all, use only that or nothing. After a superlative (the best, the first), that is also usual: It's the best film (that) I've ever seen.
That or what after a verb
After verbs like know, say, think and understand, that joins a whole sentence: subject + verb + the rest. What is a thing: it is the object of the verb in its own clause.
- I know that you're right.
(A whole sentence follows: you're right.)
- I know what you mean.
(What is the object of mean.)
- Incorrect: I know what you are right.
- Correct: I know that you are right.You are right is complete, with nothing missing, so use that.
- Incorrect: I didn't hear that she said.
- Correct: I didn't hear what she said.Said needs an object, and what is that object.
Which for a whole clause
To refer back to the whole of the first part of a sentence, use which, after a comma. What is not possible here.
- He arrived late again, which annoyed everyone.
- Incorrect: She didn't apologise, what was rude.
- Correct: She didn't apologise, which was rude.To comment on the whole first part, use which.
A what clause can begin a sentence instead: What annoyed everyone was that he arrived late again.
What at the start for emphasis
Starting with a what clause and is / was puts the focus on the end of the sentence.
- What I like about her is her honesty.
- What we need is more time.
- What surprised me was the price.
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Related rules
Where this rule sits
All B2 rulesClauses and linking words: all rules