since 在状语从句中的用法

一、当since引导的状语从句的谓语动词是瞬时动词的过去时,则从句表示的时间是从“动作开始的那一时刻”起.
如：He has studied very hard since he came to our school.
自从来到我们学校,他学习非常刻苦.
We have been missing them since they left here.
自从他们离开这儿,我们就一直想念他们.
二、若since引导的状语从句的谓语动词是持续性动词或者是表示状态的动词的过去时时,则从句表示的时间是从“持续动作或状态结束的时刻”算起.
如：I haven’t heard any noise since I slept.
sleep为持续性动词,sleep的动作结束的时候,也就是“醒来”时,所以这句话的翻译为“我醒来后一直没有听到任何声响”.
John is now with his parents in New York,it is already three years since he was a teacher.
John现在和他父母一起住在纽约,他不当教师已经三年了.
三、若since引导的状语从句的谓语为持续性动词的现在完成时,则表示动作和状态延续到现在,从句的时间起点应该从“持续动作发生的时刻”算起.
如：I haven’t heard from him since he has lived there.
自从他住在那儿后,我就一直没有他的消息了.
Since we have owned a car,we have gone camping every year.
自从我们有车后,我们每年都出去野营.
比较：
Since I've been at this school,we have had three headmasters.我到这个学校后,我们换了三个校长.
Since I was at this school,they have had three headmasters.我离开这个学校后,他们换了三个校长.
He has never been to see me since I have been ill.我生病以来,他一直没来看过我.
He has never been to see me since I was ill.我病好后,他一直没来看过我.
四、至于It is +一段时间+since…的句型与It has been +一段时间+since…意思相同.前者是规范说法,後者是口语说法.
应注意的是,在这种结构中,since引导的从句绝对不能用否定式的谓语动词来表示否定意义,下面两句都错了：
It is a long time since he didn't study English.
It's two months since you didn't come to see me.
正确的说法为：
It's a long time since he studied English 他好久没学英语了.
You haven't come to see me for two months.你有两个月没来看我了