I am not always sure how to check if a relative clause is essential (defining) or non-essential (non-defining).
Let's take this example from MGMAT's SC
book, pages 93 and 97, 12th edition:Well-informed people know that Bordeaux is a French region whose most famous export is the wine that bears its name
I am interested in the underlined relative clause that modifies region
. Is this clause essential or non-essential?
This clause can be considered non-essential because...
- because of the indefinite article "a" in "a French region". After all, the sentence could have said "the French region famous for its same=named wine".
- because even without this modifier it is still clear, which French region is meant.
This clause can be considered essential because...
- because there is no comma before whose. Do we need one?
- because if we remove the clause, the meaning of the sentence changes. Well-informed people know that Bordeaux is a French region.
Now those people do not look that informed any more.
The modifier could be essential as well as non-essential. You should use the one based on the meaning that you want to express. You can identify whether a relative clause is non-essential by the use of comma. In the example that you have used the relative clause would be considered an essential one as it does not contain comma.
The person, who is standing next to the white car, is my brother.
The person who is standing next to the white car is my brother.