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Relative Pronouns in Non-defining Clauses

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Non-defining relative clauses (also known as non-restrictive, or parenthetical, clauses) provide some additional information that is not essential and may be omitted without affecting the contents of the sentence. All relative pronouns EXCEPT that can be used in non-defining clauses; however, the pronouns MAY NOT be omitted. Non-defining clauses ARE separated by commas.

The table below sums up the use of relative pronouns in non-defining clauses:

Function in
the sentence
Reference to
People Things / concepts Place Time Reason
Subject who which
Object who, whom which where when why
Possessive whose whose, of which
  1. Relative pronoun used as a subject:

    The writer, who lives in this luxurious mansion, has just published his second novel.

  2. Relative pronoun used as an object:

    The house at the end of the street, which my grandfather built, needs renovating.

  3. Relative pronoun used as a possessive:

    William Kellogg, whose name has become a famous breakfast foods brand-name, had some weird ideas about raising children.

Some special uses of relative pronouns in non-defining clauses

  1. which
    If you are referring to the previous clause as a whole, use which :

    My friend eventually decided to get divorced, which upset me a lot.

  2. of whom, of which
    Use of whom for persons and of which for things or concepts after numbers and words such as most, many, some, both, none:

    I saw a lot of new people at the party, some of whom seemed familiar.
    He was always coming up with new ideas, most of which were absolutely impracticable.