Some relative clauses refer to a whole clause, a whole sentence, or a longer stretch of language. We always usewhichto introduce these clauses.
We often use these clauses in informal speaking to express an opinion or evaluation (In the examples, the relative clause is inbold, and the clause or person that is referred to isunderlined.):
I think the other thing that was really good about it as well was thateverybody worked really hard and helped tidy up at the end,which I hadn’t expected at all.
In speaking, a second speaker often uses awhich-clause like this to evaluate or give an opinion on something the first speaker has said:
[The speakers are talking about trains. Paddington is a train station in London.]
A:So it leaves Paddington at 8.30 andit’ll get me into Gloucester at 10.15.
B:Which is perfectbecause I can pick you up on my way home. (Speaker B is evaluating the fact that the train gets into Gloucester at 10.15.)
Sometimes the same speaker may add awhich-clause after a response by a listener:
A:I was already working with them doing a temporary job and I was asked ifI would go on a permanent contract.
B:Oh right.
A:Which I did. (Speaker A was offered a permanent job contract and accepted the offer.)
In speaking we sometimes pause before these clauses:
She just lives six doors away, [pause]which is very handy.