In English non defining relative clauses may be omitted without affecting the understanding of the phrase. They are not essential because they do not define the noun but they add some further information. Non defining relative clauses are usually expressed within commas.

Subject Pronouns Object pronouns Possessive pronouns Examples
People    
Who who/whom whose
  • The man, who had been driving without licence, was fined by the police.
  • The boy, whom I spoke you about, is a very good dancer.
  • Peter, whose car I borrowed, told to drive carefully.
Things      
which which whose/of which
  • The classroom, whose windows had been left open, was all in a mess because of the strong wind blowing through them.
  • The truck, which collided against the guard rail, tore it completely apart.

 

Pay attention!

Relative pronouns may be omitted when they are the object of a relative clause and when there is a preposition. They cannot be omitted if they are the subject of the relative clause. – The girl (whom) I lent my laptop to didn’t turn up.

 

– The boys, who were at the party, began to drink heavily.
Non defining relative clause