Defining and non-defining adjective clauses

Sometimes the relative pronoun or the relative adverb introducing an adjective clause is understood and is hence omitted.

Examples are:

  • This is all I have. (= This is all that/which I have.)
  • Here is the camera I promised to give you. (= Here is the camera which / that I promised to give you.)
  • The reason she hates me is unknown to me. (= The reason why she hates me is unknown to me.)

An adjective clause may be defining or non-defining.

A defining adjective clause clearly identifies its antecedent whereas a non-defining adjective clause merely gives some information. In writing, non-defining adjective clauses are always separated by commas.

Examples of defining relative clauses are:

  • There are the keys that you were looking for.
  • This is the house that Jack built.

Examples of non-defining relative clauses are:

  • Susan, who is a well-known social activist, is a brave woman.

Here the adjective clause ‘who is a well-known social activist’ merely gives some additional information about Susan. Hence it is a non-defining adjective clause.

  • Jack, who is my friend, lives abroad.

Here the adjective clause ‘who is my friend’ is non-defining because it merely adds some additional information.


The relative pronoun can sometimes be omitted in the case of a defining relative clause.

  • The book you gave me was very interesting. OR The book which you gave me was very interesting.

The relative pronoun introducing a non-defining adjective clause cannot be left out.

  • Susie, who is my sister, is a doctor. (NOT Susie is my sister is a doctor.)

Note that a non-defining adjective clause can be left out from the sentence without altering its meaning.