These snacks, which are so easy to make, are absolutely delicious. These snacks, which are so easy to make, are absolutely delicious.
We sometimes use a relative clause in order to add a little extra, unnecessary information.
In these kinds of sentences, the clause is often in the middle of a sentence, with a comma before and after it.
My manager, who prefers bigger teams, wants to recruit more staff.
Our most recent project, which took two years to complete, was very successful.
If we remove the relative clause, the meaning of the sentence remains clear - we know which manager and project we are talking about:
My manager wants to recruit more staff.
Our most recent project was very successful.
So, there is a difference between these two sentences:
1. My sister, who lives in Paris, is an architect.
2. My sister who lives in Paris is an architect.
In sentence number 1. we know which sister we are talking about - maybe there is only one sister or it is already clear which one we are referring to. We could just say:
My sister is an architect.
In sentence number 2. the speaker has more than one sister and uses a defining relative clause to tell us which one is an architect. It is the one who lives in Paris.
As well as putting the clause in the middle of a sentence between two commas, we can also put it at the end of a sentence:
Our most recent project was successful, which made us all very happy.
She went on holiday to Italy, where her son lives.
Remember that in non-defining relative clauses, we cannot use that. We have to use who or which. Compare a non-defining and defining relative clause:
He cooked a meal for us last night, which was unusual. [He doesn't usually cook.]
He cooked a meal for us last night which/that was unusual. [The meal was unusual.]
This can be confusing because you might think you are hearing two separate sentences instead of a relative clause. We can, in fact, have two separate sentences but with 'that' as a demonstrative pronoun:
He cooked a meal for us last night. That was unusual. [He doesn't usually cook.]
Note that
1. in non-defining relative clauses, we cannot use that. We have to use who or which.
My sister, who lives in Paris, is an architect. 
My sister, that lives in Paris, is an architect. 
My sister who/that lives in Paris is an architect.
2. it is never possible to omit which and who in non-defining relative clauses:
My daughters, who are both students, live at home with me.
My daughters, who are both students, live at home with me.
The meeting, which was on Monday, wasn't very productive.
The meeting, which was on Monday, wasn't very productive.
3. the rules regarding who and whom are the same as for defining relative clauses :
My manager, whom/who I really like, is retiring next year.
My manager, who prefers bigger teams, wants to recruit more staff.
If there is any doubt, it is better to use who because it is much more commonly used than whom - both spoken and written.
4. We can use where and whose in non-defining relative clauses:
I'm going to Venice, where I first met my husband, with some friends next year.
The book, whose author is Mexican, is a best-seller.
5. We can use prepositions in non-defining relative clauses:
Our manager, for whom we have a lot of respect, always listens to our problems. [formal]
Our manager, who we have a lot of respect for, always listens to our problems. [conversational]
=====Examples=====
The people in this picture, who/whom I met at university, all live in the USA now.
I have four children. My daughters, who are both students, live at home with me.
"How was your trip?" "It rained all week, which wasn't pleasant, but we agreed on a deal."
Hello everyone. My name's Peter and I'm in charge of the innovation department, whose main target is to suggest new services for our portfolio.
Sydney, where I worked after graduating, is an amazing city.
Reduced relative clauses
In order to make certain relative clauses more succinct, we omit both the pronoun and the verb. Here are some examples:
|
| Full sentence | Reduced sentence |
| With a past participle
Note that the participle remains the same whether we are talking about the past, present or future. | The equipment, which was needed for this job, arrived yesterday.
Some data, which was known to be incorrect, was used so that the report could be completed on time.
| The equipment, needed for this job, arrived yesterday.
Some data, known to be incorrect, was used so that the report could be completed on time.
|
| With adjectives | The device, which was innovative at the time, is no longer used.
| The device, innovative at the time, is no longer used. |
Flamenco dancing, not easy to do, is great to watch.
Writing notes on someone's business card, considered impolite in Japanese culture, is quite acceptable in Europe.
