You can see if a relative clause is defining or non-defining by removing it from the sentence.
If you remove a defining relative clause, the sentence has a different meaning or is incomplete. - That’s the student who failed English class three times
If you remove a non-defining relative clause, the sentence still has the same meaning. - My brother, who lives in California, is an engineer.
A relative clause is a phrase that adds information to a sentence. All relative clauses describe a noun, and they begin with one of these relative pronouns or relative adverbs.
which (to describe things – non-defining relative clauses)
that (to describe things – defining relative clauses)
whose (to describe possession)
whom (to describe people – object)
who (to describe people – subject)
Relative Pronouns
which or that
Use that for defining relative clauses, and don’t use a comma before it. -The bananas that I bought on Monday are rotten.
Use which for non-defining relative clauses, and use a comma before it.
- The bananas, which I bought on Monday, are rotten.
