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READY | Grammar & Writing
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Defining relative clauses
are necessary if we want to understand the meaning of a sentence.
I saw the girl who was outside our house. (necessary information)
If we leave them out, it is not clear what girl we are talking about.
*Do not write them with commas.
Non-defining relative clauses
only add some extra information, which is not necessary.
My father, who is 65 now, still works. (unnecessary information)
If we leave them out, it is still clear what father we are talking about.
*They must be written with commas.
WATCH OUT
“That” cannot be used to introduce a non-defining relative clause (with commas)
- ❌ Neil Amstrong, that was born in 1930, was the first man to stand on the moon.
- ✅ Neil Amstrong, who was born in 1930, was the first man to stand on the moon.