See also Pronouns
There are two different types of relative clause:
- A "defining" or identifying clause, which tells us which person or thing we are talking about. This kind of clause could often be information included in brackets (...)
- A "non-defining" or non-essential clause, which gives us more information about the person or thing we are talking about.
- The farmer (his name was Fred) sold us some potatoes. The farmer, whose name was Fred, sold us some potatoes.
It is important to see the difference between the two types of clause, as it affects:
- the choice of pronoun used to introduce the clause,
- the punctuation - you must use commas with a non-defining clause.