Defining relative clauses provide essential information about the person or thing we are discussing. They don’t require commas.
Example
- This is the music which was used at the show.
- Have they found the prisoner who escaped last week?
In defining relative clauses, we can use that instead of which or who.
Example
- This is the music that was used at the show.
- Have they found the prisoner that escaped last week?
When a clause follows a subject-verb structure, the relative pronoun (who/which/that) can be omitted.
Example
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.
References