When we want to give a reason for a particular situation, we can begin a clause with as, because, since, etc. As, because and since are conjunctions and they all introduce subordinate clauses. They connect the result of something with its reason.
As it was getting late, [reason] we decided to take a cab to the airport. [result]
We must get out of the car, [result] because I can hear some strange noises. [reason]
Since she was going to be living in Canada for good, [reason] she thought she should dispose of all household goods. [result]
We use as when we want to focus more on the result than the reason. As is relatively more formal than because:
As she was getting late, [reason] we decided to let her go first. [result]
We let him take the elevator [result] as he looked older. [reason]
She asked the teacher if she could be excused from singing practice as her throat was still sore.
Improved safety measures in factories can be counterproductive as they encourage employers to increase the working hours.
As you’re in charge here, you’d better tell me where to go.
We often use as clauses at the beginning of the sentence. We use a comma after the as– clause:
As you are leaving last, lock the door.
As they already knew each other, there were no formalities. We got straight into the business of the meeting.
Because is more common than as and since, both in writing and spoken English. When we use because, we are focusing on the reason:
She got off the bed quietly because she didn’t want to wake the child up.
We’ll celebrate Emma’s birthday on Saturday because she’s got to leave for her boarding school on Sunday.
In spoken English, we most often use because (often spoken as cos /kəz/ or /kɒz/) to give a reason. We can also use so to express the same meaning. Compare:
· Because his wife has been admitted to hospital, he won’t be able to attend this week’s meeting.
· His wife has been admitted to hospital, so he won’t be able to attend this week’s meeting.
Notice that it is also common and acceptable to begin a sentence with because especially when we want to give extra focus to the reason and we use a comma after the because-clause, as in: Because everything worked out quite the way we planned it, we decided to leave the place.
She didn’t go to the cinema because she was feeling awful. √
Since she was feeling awful, she didn’t go to the cinema. ✗ (in an informal context, since is unlikely)
We can use a because-clause on its own without the main clause in speaking or informal writing: Why do you get up so early in the morning? Because I don’t want to miss out on all the fun in the park.
Warning: We use because, not as or since, in questions where the speaker proposes a reason:
Are you feeling unwell because you couldn’t get to sleep at all last night? √
Are you feeling unwell since you couldn’t get to sleep at all last night? ✗
Are you feeling unwell as you couldn’t get to sleep at all last night? ✗
We use since when we want to focus more on the result than the reason. Since is also more formal than because. We often use since clause at the beginning of the sentence and usually put a comma before since after the main clause:
I’m forever losing things, [result] since I’m quite forgetful. [reason]
Since she did not make enough money to live in her own house, [reason] she went back to live with her mother. [result]
Since the work can be done from home with computers and telephones, there’s no need to commute to office any more.