WHAT OR THAT? 1

level: Intermediate (B1/B2)

This is one of the most common mistakes ESL learners make: using what as if it were a general-purpose relative pronoun, the way that, who, or which work. English doesn't allow this — the two words follow completely different rules, and mixing them up produces sentences that sound clearly wrong to a native speaker.

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Fill in each blank with what or that.

1. he said is not important.✓

2. The book I'm reading is very interesting.✓

3. I'm not responsible for you do.✓

4. P1: Do you believe he told us? P2: Yes, I think he was telling the truth.✓

5. The world needs more people help animals.✓

6. Tom's parents care about he watches.✓

7. Many of the people saw that movie were disappointed.✓

8. You have to let me know you plan to do.✓

9. The coffee you made is very strong.✓

10. We loved the story you told in class.✓

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Grammar review The mistake: saying something like “The book what I'm reading…” This sounds natural in some dialects and in several other languages, but it's not correct in standard English. What can never point back to a specific noun that's already there.

Use that when there's already a noun for the clause to describe (this is a normal relative clause):
“The movie that we watched was terrifying.” → the clause describes the movie
“The cake that she baked was delicious.” → the clause describes the cake

Use what when there's no noun at all, the clause itself acts as the noun, meaning "the thing(s) that…":
“What she wrote surprised everyone.” → = the thing that she wrote
“I don't understand what he wants.” → = the thing that he wants

The quick test: look at the word right before the gap. If it's a specific noun (book, coffee, people, story…), use that. If there's nothing there — just a verb, a preposition, or the start of the sentence — use what.

KEEP PRACTICING — MORE EXERCISES FOR YOU:
Relative clauses 1 (I)
Relative clauses (who, that) 1 (I)
Noun clauses 1 (I)
Noun clauses 2 (I)
Who, which, whose 1 (I)