4.since引导的时间状语从句

(1)since引导时间状语从句所表示的基本意思是“自……以来”。

Sarah and Janet have been friends ever since they started school．(人教大纲版高一上第89页)

自从她们上学以来，莎拉和珍妮特就是好朋友。

Since the first case was discovered in 1981，nearly 24 million people have died of AIDS．(人教大纲版高二上第127页)

自1981年发现第一个病例以来，已经有将近两千四百万人死于艾滋病。

I have been looking forward to seeing you since I saw you last．

自我上次见到你以来我就一直想再次见到你。

(2)since引导时间状语从句时主句的谓语动词的时态。

从上述诸例可以看出，since引导时间状语从句时，主句的谓语动词常用现在完成时。

但是在下面的情形下，可以使用一般现在时或现在进行时:

①当主句指的是某种习惯或已存在的状态时。

I'm feeling better since I took the medicine．

自服了那个药以来我感到好多了。

Since we bought the car my husband and I go camping every weekend．

自从我们买了那辆车以来，我丈夫和我每逢周末都去野营。

②含有情态动词时。

I can't go to visit my parents often since I my son was born．

自我儿子出生以来，我不能常去看我父母。

I have(had)to find a job since I lost mine last year．

自我去年失业以来我就不得不去找工作了。

③当主句动词是系动词be或seem，且其表语是一个段时间时。

Things are different since you left．

自你走后情况就不同了。

It seems a long time since I met you last．

自我上次见到你以来似乎有很长时间了。

It is twenty years since the war ended．

战争结束二十年了。

当然也可以使用现在完成时:

How long has it been(is it)since he joined the army?

他当兵几年了?

提示：

注意“It+be+段时间+since”与“It+be+段时间+before”句型的区别:①“It+be+段时间+since”表示“自……以来多长时间了”;“It+be+段时间+before”表示“过了多长时间就(才)……”。②在“It+ be+段时间+since”句型中，be动词常常是is(=has been)或was(= had been)，since从句中的动词是一般过去时(使用最多)、过去完成时或现在完成时;在“It+be+段时间+before”句型中，be动词使用was或will be，before从句使用一般过去时或一般现在时。请对比:

It is a week since he left/has left．

他离开一个星期了。

It was a week since he left/had left．

他离开一个星期了。

It was a week before he left。

过了一个星期他才离开。

It will be a week before he leaves．

要过一个星期他才离开。

(3)since引导时间状语从句中动词的终止性、延续性及从句的动词时态。

①since引导的状语从句其谓语动词是终止性的过去时，则从句表示的时间是从动作开始的那一时刻起，这是最常见的一种用法。

He has studied very hard since he came to our school．

自从他来到我校，他学习就非常努力。

We have been missing them since they left here．

自从他们离开这里，我们就一直很想念他们。

②since引导的状语从句，其谓语动词是持续性动词或表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时算起。

I haven't heard any noise since I slept．

我睡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 wasa teacher．

约翰现在和父母一起住在纽约，他不当教师已经三年了。

I have not heard from him since I lived in Shanghai．

自从我住在上海后，就再也没有收到他的信。

It's been years since I enjoyed myself so much．

我已经许多年没有这样痛快了。

请比对：

He has written to me frequently since I was ill．

自从我病愈以来，他屡次给我写信。(从句谓语为表状态的动词。)

He has written to me frequently since I fell ill．

从我生病以来，他就屡次给我写信。(从句谓语为终止性动词。)

③since引导的状语从句，其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;其谓语为终止性动词的现在完成时，与该动词使用一般过去时所表达的意思无异，即从句表示的时间是从动作开始的那一时刻起。

I haven't heard from him since he has lived there．

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 go/have gone camping every year．

自从我们自己有了汽车以来，我们每年都去野营。

It's years since he left．=It's years since he has left．

他离开多年了。

请对比：

He has written to me frequently since I was ill．

自从我病愈以来，他就经常给我写信。

He has written to me frequently since I have been ill．

从我生病以来，他就经常给我写信。

由此可见，since引导的从句中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。

④当since引导的状语从句所涉及的情景不是延续到现在，而是从过去的某一时刻延续到另一个过去的时刻，主句使用过去完成时(be动词常用was代替had been)，since从句既可使用过去完成时，也可使用一般过去时，这种情况常见于间接引语或上下文是过去的动作。

Two weeks had passed since I saw/had seen him．

看见他以后已过去两个星期了。

It was(=had been)years since I left/had left．

我离开多年了。

He said it was years since he enjoyed/had enjoyed himself．

他说他有多年没有这么痛快了。