二、若since引导的状语从句的谓语动词是持续性动词或表示状态的动词的过去时时，则从句表示的时间是“从那持续动作或状态结束时算起”。如：

　　I haven’t heard any noise since I slept. Sleep 为持续性动词，sleep的动作结束时，即“醒来”时，这句应译为“我醒后还未听到任何声音”。

　　John is now with his parents in New York, it is already three years since he was a teacher约翰现在和父母一起住在纽约，他不当老师已经三年了。

　　本文开始出现的那个句子就可以译为“自从我离开上海，就再也没有收到他的信。”这种译法常被人们误用，我们不妨再多举几个例子看看：

　　How long is it since you lived in Shanghai?你离开(没住在)上海多久了?

　　It is half a month since he was a League member.他退团(不当团员)半个月了。

　　It’s been quite some time since I was last in London我离开伦敦已很长时间了。

　　比较：He has written to me frequently since I was ill.自从我病愈以来，他屡次给我写信。(从句谓语为状态动词)

　　He has written to me frequently since I fell ill.自从我生病以来，他就屡次给我写信。(从句谓语为终止性动词)

　　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(说话时刻)，其表示的时间的起点应从动作发生之时算起。如：

　　I haven’t heard from him since he has lived there。

　　这里has lived表示动作的持续性，时间的起点应从：“开始居住”时算起。因此此句可理解为“自从他(开始)住在那儿起，我就一直没收到他的来信”。

　　Since we have owned a car, we have gone camping every year。自从我们自己有了汽车，我们每年都去野营。

　　试比较：1. Since I’ve been at this school, we have had three headmasters.自从我到这所学校，我们已换了三个校长了。

　　Since I was at this school, they have had three headmasters.自从我离开这所学校，他们已换了三个校长了。

　　2.He has never been to see me since I have been ill. 自从我生病以来，他从未来看过我。

　　He has never been to see me since I was ill. 自从我病愈以来，他从未来看过我。

　　由此可见，since引导的从句持续动词的一般过去时和现在完成时所表示的意思恰好相反。换言之，前者以肯定的语法形式反映着否定的逻辑内容，而后者的形式与内容是一致的。

　　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，后者是口语说法。

　　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