8.18 When something is the case because of a new situation, you can say what is the case and then add a subordinate clause saying what the new situation is. The subordinate clause begins with now that. In British English you can leave out that.
He could travel much faster now that he was alone.
I feel better now I’ve talked to you.
saying when a situation began
8.19 If you want to say that a situation started to exist at a particular time and still exists, you use since or ever since. In the time clause, you use the past simple.
I’ve been in politics since I was at university.
It’s been making money ever since it opened.
You also use since or ever since to say that a situation started to exist at a particular time, and still existed at a later time. In the time clause, you use the past simple or the past perfect.
He had been tired ever since he started work.
Janine had been busy ever since she had heard the news.
If you are mentioning someone’s age at the time when a situation started, you always use the past simple.
I was seven years older than Wendy and had known her since she was twelve.
Since is also used in reason clauses. This is explained in paragraph 8.50.
saying when a situation ends
8.20 If you want to say that a situation stopped when something happened, you use until or till.
I stayed there talking to them until I saw Sam Ward leave the building.
We waited till they arrived.
You also use until or till to say that a situation will stop when something happens in the future. In the time clause you use the present simple or the present perfect.
Stay with me until I go.
We’ll support them till they find work.
Tell him I won’t discuss anything until I’ve spoken to my wife.
8.21 By which time, at which point, after which, whereupon, and upon which are also used at the beginning of time clauses.
You use by which time to say that something had already happened or will already have happened before the event you have just mentioned.
He was diagnosed in 1999, by which time he was already very ill.
You use at which point to say that something happened immediately after the event you have just mentioned.
The company closed in the late seventies, at which point he retired.
You use after which to say that a situation started to exist or will start to exist after the event you have just mentioned.
The items were removed for chemical analysis, after which they were never seen again.
You use whereupon or upon which to say that something happened immediately after the event you have just mentioned and was a result of it. Both of these uses are rather formal.
His department was shut down, whereupon he returned to Calcutta.
I told Dr Johnson of this, upon which he called for Joseph.
8.22 You can use a clause beginning with when after a question beginning with why. For example, you can say Why should I help her when she never helps me? However this clause is not a time clause. In your question, you are expressing surprise or disagreement at something that has been said, and the when-clause indicates the reason for your surprise or disagreement.
Why should he do me an injury when he has already saved my life?
Why worry her when it’s all over?
using non-finite clauses
8.23 Instead of using a finite time clause, you can often use a non-finite clause, that is, a clause that contains an -ing or -ed participle.
For example, you can say I often read a book when travelling by train, meaning I often read a book when I am travelling by train, and you can say When finished, the building will be opened by the Prince of Wales, meaning When it is finished, the building will be opened by the Prince of Wales.
Adults sometimes do not realize their own strength when dealing with children.
Mark watched us while pretending not to.
I deliberately didn’t read the book before going to see the film.
After complaining of a headache for a few days, Gerry agreed to see a doctor.
They had not spoken a word since leaving the party.
Michael used to look surprised when praised.
Once convinced about an idea, he pursued it relentlessly.
Note that you can only use a clause like this when it does not need to have a new subject, that is, when it is about the same thing as the main clause.
using prepositional phrases and adjectives
8.24 For some statements about time, you can use a phrase consisting of when, while, once, until, or till, followed by a prepositional phrase or an adjective.
For example, you can say, When in Paris, you should visit the Louvre, meaning When you are in Paris, you should visit the Louvre.
He had read of her experiences while at Oxford.
When under threat, they can become violent.
Steam or boil them until just tender.
You can use a phrase consisting of when, whenever, where, or wherever and an adjective such as necessary or possible.
For example, you can say You should take exercise whenever possible, meaning You should take exercise whenever it is possible.
She spoke rarely, and then only when necessary.
Try to speak the truth whenever possible.
Help must be given where necessary.