تويت
Look at the two sentences
London has over 6 million inhabitants
London , which is the capital of Britain , has over 6
Million inhabitants
The clause which is the capital of Britain gives us more information about London, but we do not need this information to define London. We can understand the first sentence without this extra information which is the capital of Britain is a non-defining relative clause. It has commas (,) to separate it from the rest of the sentence
For things or animals, we use which (but not that) in non-defining relative clauses: Fred sold his computer, which he no longer needed, to his cousin .(Not ……. That he no longer needed…)
In the summer we stay in my uncle's house, which is near the sea
For people, we use who (but no that) in non-defining relative clauses . We use who when it is the subject of the relative clause
Elvis Presley, who (subject) died in 1977, earned millions of dollars
We use (or sometimes whom) when it is the object of the relative clause
My boss, who or whom (object) I last saw before Christmas, is very ill
(I last saw my boss before Christmas.)….
We use whose to mean his or her or their
Al-Mahdi, whose real name was Muhammad
We can also use which (but not that) to refer to a whole fact: Ann did not want to marry Tom, which surprised everybody
Here, which refers to the fact that Ann did not want to marry Tom