Non-defining relative clauses

As the name suggests, non-defining relative clauses tell us more about someone or something, but the information in these clauses does not help us to define what we are talking about.Take for example the sentence: Gorillas, which are large and originate in Africa, can sometimes be found in zoos. In this sentence we are talking about all gorillas, not just some of them. The information in the non-defining relative clause tells us something more about gorillas in general. It does not define a small group of gorillas or an individual gorilla. If the non-defining relative clause were removed from the sentence, the sentence would still be gramatically correct and the meaning would not have changed, although we would have less detail.

Non-defining relative clauses are composed of a relative pronoun, a verb, and optional other elements such as the subject or object of the verb. Commas or parentheses are always used to separate non-defining relative clauses from the rest of the sentence.

Examples
  • John's mother, who lives in Scotland, has 6 grandchildren.
  • My friend John, who went to the same school as me, has just written a best-selling novel.
  • My grandmother, who is dead now, came from the North of England.
  • We stopped at the museum, which we had never visited before.
  • I've just come back from London, where John lives..
  • Yesterday I met a woman named Susan, whose husband works in London.

Relative pronouns

The following relative pronouns are used in non-defining relative clauses. These relative pronouns appear at the start of the non-defining relative clause and refer to a noun that appears earlier in the sentence.

  Person Thing Place
Subject who which  
Object who/whom which where
Possessive whose    
Differences with defining relative clauses

In defining relative clauses, the pronouns who, whom, and which are often replaced by that in spoken English. In non-defining relative clauses, you cannot replace other pronouns with that. You also cannot leave out the relative pronoun in non-defining relative clauses, in the way you sometimes can in defining relative clauses. The pronoun is required, even when it is the object of the verb in the relative clause. Finally, non-defining relative clauses are always separated from the rest of the sentence by commas, unlike defining relative clauses, which have no punctuation.

Examples
  • He gave me the letter, which was in a blue envelope. (non-defining clause: There was only one letter, it happened to be blue. You must use which)
  • He gave me the letter which/that was in a blue envelope. (defining clause: There were several letters of different colors and he gave me the blue one. Which may be replaced by that. The commas are removed.)
  • He gave me the letter, which I read immediately. (non-defining clause: There was only one letter. which is the object of read, but it still must be included in the sentence.)
  • Stratford-on-Avon, which many people have written about, is Shakespeare's birthplace. (Any preposition that appears is normally placed at the end of the clause.)
  • Stratford-on-Avon, about which many people have written, is Shakespeare's birthplace. (In formal written English, you can also put the preposition before the pronoun.)
Introductory expressions in non-defining clauses

Non-defining clauses can be introduced by expressions like all of or many of followed by the relative pronoun.

  Person Thing
all of, any of, some of, a few of, both of, each of, either of, half of, many of, most of, much of, none of, one of, two of, etc. whom which
Examples
  • There were a lot of people at the party, many of whom I had known for years.
  • There are 14 girls in my class, a few of whom are my friends.
  • He was carrying his belongings, many of which were broken.
  • He had thousands of books, most of which he had read.
  • He picked up a handful of stones, one of which was sharp.
Using "which" to refer to another clause

The relative pronoun which at the beginning of a non-defining relative clause can refer to all the information contained in the previous part of the sentence, rather than to just one word.

Examples
  • Chris did really well in his exams, which is quite a surprise.
  • My friends were all hiding in my apartment, which isn't what I'd expected.
  • She's studying to become a doctor, which is difficult.
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