Defining no Defining relative clauses, Explicación

Defining relative clauses

Defining relative clauses carry essential information, because they identify which thing or person we are talking about, and they are used without commas.

• This is the music which was used at the show. 
• Have they found the prisoner who escaped last week?

We can use that

In defining relative clauses we can use that instead of which or who.

• This is the music that was used at the show. 
• Have they found the prisoner that escaped last week?

When can we omit who/which/that?

Who/which/that, can be omitted if they are followed by subject + verb

• Can you pass me the box (which/that) I keep in the top drawer?
• You are not the man (who/that) I thought you were. 

Non-defining relative clauses

Non-defining relative clauses are used between commas, and they add extra information which is not necessary to know who or what we are talking about.

• This music, which I really like, was used at the show.
• My sister, who I truly admire, is coming for Thanksgiving. 

We cannot use that, and we cannot omit who/which

In non-defining relative clauses (between commas) we cannot use that, and we cannot omit who/which.

• This music, that I really like, was used at the show. 
• My sister, I truly admire, is coming for Thanksgiving. 

Defining vs non-defining relative clauses

In a defining relative clause the information is essential to identify who or what we are talking about, whereas in non-defining relative clauses we just add extra the information, which is not necessary. Compare:

• My brother who lives in Cardiff is much older than me. (=I have more than one brother and the relative clause helps identify which brother I am talking about)
• My brother, who lives in Cardiff, is much older than me. (=I have only one brother, so we don’t need the relative clause to know who I am talking about)