Defining and non-defining clauses are both types of relative clauses – clauses that share some extra information.
Relative clauses state additional information about the noun in the sentence.
- Plastic producers who supply us with lots of things seem to have found their way into every single aspect of our lives.
The phrase "who supply us with lots of things" adds some extra information to the sentence, so you can understand a little more about the subject, the producers.
Defining relative clause adds detail about a specific noun that is defined.
- My brother who brings his eco grocery bag to the supermarket for 5 years now is taking part in our zero-waste conference too.
LED light bulbs whose efficiency is rather high last longer than conventional bulbs.
In both the examples above, you can see an extra clause in the middle of the sentence following the words "who" or "whose" which contain additional information. They relate to a specific noun that has been pointed out: "my brother" or "LED light bulbs".
Defining relative clauses use a relative pronoun such as:
Note: without the additional clause, the sentence would not retain the same meaning.
- They're the people who want go eco-friendlier.
- Here are the areas of the planet which have been affected.
In writing, we don't use commas in defining relative clauses:
Non-defining relative clause still adds extra information, but not in the same way.
It tells you something additional, but it isn't necessary to the meaning of the sentence.
- A lot of cleaning products, which are found on the supermarkets shelves, have harmful chemicals that aren't environmentally friendly to use or dispose of
While the clause certainly tells you something interesting about the topic, the sentence would still retain the main meaning without it:
A lot of cleaning products have harmful chemicals that aren't environmentally friendly to use or dispose of
Non-defining clauses also use relative pronouns, just as defining clauses do. The only difference is that you cannot use "that" with a non-defining clause, unlike defining clauses.
It's easy to spot a non-defining clause in writing, as you'll see that the clause is separated by commas at the start and end of it.
Sometimes defining and non-defining relative clauses can look very similar but have different meanings.