Non-defining relative clauses provide extra information about a person or thing being referred to that is not essential for identifying them. They are usually separated from the main clause by commas. Relative pronouns like 'who', 'which', 'whom', and 'that' are used to begin non-defining relative clauses, with 'who' and 'whom' used for people and 'which' used for things. 'When' and 'where' can also be used in non-defining relative clauses after expressions of time and place.

1. Non-defining
Relative Clauses

2. Non-defining Relative Clauses
You use non-defining relative clauses to give
extra information about the person or thing
you are a talking about. The information is
not needed to identify that person or thing.
Professor Marvin, who was always early,
was there already.

3. Non-defining Relative Clauses
Professor Marvin, who was always early,
was there already.
‘Who was always early’ gives extra
information about professor Marvin. This is a
non-defining relative clause, because it is not
needed to identify the person you are talking
about. We already know that you are talking
about Professor Marvin.

4. Non-defining Relative Clauses
Note: In written English, a non-defining
relative clause is usually separated from the
main clause by a comma, or by two commas.
I went to the cinema with Mary, who I think
you met.
British Rail, which has launched an inquiry,
said one coach was badly damaged.

5. Non-defining Relative Clauses
You always start a non-defining relative
clause with a relative pronoun. When you are
talking about people, you use ‘who’. ‘Who’ can
be the subject or the object of a non-defining
relative clause.
She was engaged to a sailor, whom she had
met at Dartmouth.

6. Non-defining Relative Clauses
When you are talking about things, you use
‘which’ as the subject or object of a non-
defining relative clause.
I man teaching at the Selly Oak centre, which
is just over the road.
He was a man of considerable inherited
wealth, which he ultimately spent on his
experiments.

7. Non-defining Relative Clauses
WARNING: You do not normally use ‘that’ in
non-defining relative clauses.

8. Non-defining Relative Clauses
You can also use a non-defining relative
clause beginning with ‘which’ to say
something about the whole situation
described in the main clause.
I never met Brando again, which was a pity.
She was a little tense, which was
understandable.

9. Non-defining Relative Clauses
When you are talking about a group of people
or things and then want to say something
about only some of them, you can use one of
the following expression:
many of which non of whom
some of which many of whom
one of which some of whom
none of which one of whom

10. Non-defining Relative Clauses
They were all friends, many of whom had
known eachother for years.
He talked about several very interesting
people, some of whom he was still in contact
with.

11. Non-defining Relative Clauses
You can use ‘when’ and ‘where’ in non-
defining relative clauses after expressions of
time or place.
This happened in 1957, when I was still a
baby.
She has just come back from holiday in Crete,
where Alex and I went last year.