(一)when, while 和 as 引导时间状语从句的用法

一、when 的用法

如果只从现象来看，when 从句用的最多的是一般过去时，而主句的时态没有限制,根据具体情况而定。

1. When he was a child he was always trying out new ideas.他小时候就常常试验一些新的设想。

2. When she came into my room, I was just reading a book. 她走进我房间时，我正在看书。

3. Were you writing when the teacher came in? 老师进来的时候，你在写信吗?

4. Sorry, I was out when you called me. 对不起，你打电话来的时候我出去了。

5. He was on the point of leaving when someone knocked at the door.他正要走，这时有人敲门。

6. I thought of it just when you opened your mouth. 就在你要说话的时候，我也想到了。

7. I had hardly[scarcely] closed my eyes when someone knocked at the door.我刚一闭上眼，就有人在敲门了。

根据以上的例句，我们可以总结出一点：when 从句的A事件，相当于另一个事件B发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间点，所以when 多数情况下用的是一般过去时，则不用正在进行时。因为如果用正在进行时，它表示的就是一段时间而不是一个时间点了。根据这一点，有的文章补充说：when 从句的动词大多是瞬时动词。这种说法也可以参照。

实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时间参照点。例如：

1. When I got to the airport, the guests had left. 当我赶到飞机场时，客人们已经离开了。

2. When he had finished his homework, he took a short rest.当他完成作业后，他休息了一会儿。

3. Why do you want a new job when you have got such a good one already?你已经找到如此好的工作，为何还想再找新的?

4. You shall borrow the book when I have finished reading it.在我读完这本书后，你可以借阅。

5. When the manager comes here for a visit next week, I’ll talk with him about this.下周，经理来这参观时，我会和他谈谈此事。

二、while 的用法

相比于when 来说，while 从句的侧重点就不一样了。while 从句的侧重点在于描述动作正在发生的状态，它的意思是：当while 事件正在发生的时候，另一件事如何如何。所以，while 从句一般用的是正在进行时。而另一件事的状态没有硬性的要求，根据具体情况而定。例如：

1. While my wife was reading the newspaper, I was watching TV.当妻子正在看报纸的时候，我正在看电视。

2. While Jim was mending his bike, Lin Tao came to see him.正当吉姆修自行车时，林涛来看他。

3. While they were talking, the bell rang. 正在他们谈话的时候，上课铃响了。

4. You can’t do your homework while you’re watching TV.你不能一边看电视一边做家庭作业。

5. While John was sitting biting his nails, I was working out a plan to get us home.约翰坐在那里咬指甲时，我正在制定一个回家的计划。

从时间的角度来看，while 表示的是一段时间，是一个过程。这是while 的侧重点。因此，如果含有“一段时间”的含义的时候，就可以用while。

6. Strike while the iron is hot. 趁热打铁。

这句话中，是说趁着铁是热的这段时间，赶紧打铁。如果换成 when 意思就变了，相当于说铁只热了一下，打一下，然后铁就冷了。这显然不符合文意。

再例：

—I'm going to the post office.

—While you're there, can you get me some stamps?

三、as 的用法

as 从句表示的也是一件事情正在发生，另一件事也正在进行当中。但与 while 从句不同的是，as 从句用的一般不用正在进行时，而只是一般过去时。as 从句一般可以翻译成“边……边……”。例如：

1. As my mother sang those old songs, tears ran down her cheeks.当我妈妈唱起那些老歌时，眼泪顺着她的脸颊流了下来。

2. The students took notes as they listened. 学生们边听课边做笔记。

3. As we talked >我们继续往下谈的时候，他越来越兴奋。

4. The little girls sang as they went. 小姑娘们一边走，一边唱。

5. Just as he caught the ball, there was a tearing sound.当他抓住球的时候，有一种撕裂的声音。

as 表达的事件，往往只是主句动作发生的背景或条件时，as 只是一个次要的时间说明，不像while 从句有强调 while 动作本身的意思。因此，as 常常翻译成“随着……”之意。

例如：

1. As the time went >，the weather got worse. 随着时间的推移，气候更加糟糕。

2. The atmosphere gets thinner and thinner as the height increases.随着高度的增加，大气越来越稀薄。

3. As years go by，China is getting stronger and richer.随着时间一年一年过去，中国变得越来越富强了。

少数情况下，如果强调动作正在发生，as 从句也可以用正在进行时。这只能算是特例了。

1. The sad mother sat on the roadside, shouting as she was crying.伤心的妈妈坐在路边，边哭边叫喊。

2. As we were going out, it began to snow. 正当我们出门时，雪开始下起来。

3. He came in as I was going to bed. 我正要上床睡觉，他进来了。

四、when, while, as 的互换

如果从句动作和主句动作同时发生，并且从句动作为延续性动词时，when，while，as 可以互换使用。

1. When /While /As we were dancing, a stranger came in. 当我们跳舞时，一位陌生人走了进来。[dance 为延续性动词]

2. When /While /As she was making a phone call, I was writing a letter.当她在打电话时，我正在写信。[make为延续性动词]

3. While/When/ As I was walking down the street, I noticed a police car in front of thebank.我顺着马路往前走时，发现银行门前停着一辆警车。

五、比较while, when, as

1)as, when 引导短暂性动作的动词。

例如：Just as / Just when / When I stopped my car, a man came up to me.我刹车后，有一个人向我走来。

2)当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。

例如：When you have finished your work, you may have a rest.干完活后，你可以休息一下。

3)从句表示“随时间推移”连词能用as，不用when 或while。例如：As the day went >　日子一天天过去，天气越变越坏。

(二)before和after引导的时间状语从句

Before是主句动作发生在从句的前面。注意before引导的从句不再用否定式的谓语，并且当before引导的从句位于主句之后，有时译成“就，才”。还要注意主句和从句之间的时间关系。当主句用将来时，从句总是用现在时;如果before引导的从句谓语用的是过去时，则主句动词多用过去完成时，这样以便体现动作发生的先后。

After表示主句动作发生在从句动作之后。主句和从句的动作的时间关系正好与before引导的从句相反。例如：

It will be four days before they come back. 他们要过四天才能回来。

Einstein almost knocked me down before he saw me.爱因斯坦几乎把我撞倒才看到我。

My father had left for Canada just before the letter arrived.我父亲恰好在信到之前去加拿大了。

They had not been married four months before they were divorced. 他们结婚还不到四个月就离婚了。

After you think it over, please let me know what you decide.你仔细考虑过以后，告诉我你是怎样决定的。

After we had finished the work, we went home.完成工作之后，我们回家了。(从句用过去完成时，主句用一般过去时)

(三)比较until和till 的用法

此两个连词意义相同。肯定形式表示的意思是“做某事直至某时”，动词必须是延续性的。否定形式表达的意思是“直至某时才做某事”。动词为延续性或非延续性都可以。正确使用这两个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。

肯定句：I slept until midnight. 我一直睡到半夜时醒了。

Wait till I call you. 等着我叫你。(在肯定句中可用before代替。

例如

：Let's get in the wheat before the sun sets.)

否定句：She didn't arrive until 6 o'clock. 她直到6点才到。

Don't get off the bus until it has stopped. 公共汽车停稳后再下车。

I didn't manage to do it until you had explained how. 直到你教我后，我才会做。

区别：1)until可用于句首，而till通常不用于句首。

例如：Until you told me, I had heard nothing of what happened. 直到你告诉我以前，出了什么事我一点也不知道。

2)until when 疑问句中，until要放在句首。

例如：

---Until when are you staying?

你呆到什么时候?

--- Until next Monday.　呆到下周一。

注意：否定句可用另外两种句式表示。

3)Not until…在句首，主句用倒装。

例如：

Not until the early years of the 19th century did man know what heat is. 直到19 世纪初，人类才知道热为何物。

Not until I began to work did I realize how much time I had wasted. 直到工作，才认识到我已蹉跎了许多岁月。

4)It is not until… that….

例如：It was not until I began to work that I realized how much time I had wasted.

(四)巧辨before和until

在日常英语教学中，我们遇到学生问这样的一些问题：

1.He will spend six hours at his desk____he finishes his composition.

A.before　　B.until　　C.after　　D.when

2.The bike hit the tree____I could get off.

A.when　　　B.before　　 C.while　　D.until

3.I knocked at the door for more than five minutes____Mrs white answered it.

A.until　　B.when　　 C.after　　D.before

4.It was____yesterday____be____the secret.

A.not until;that;knew　　　B.until;when;knew

C.not before;that;found　　D.before;that;didn't find

怎样才能清楚地解释其选择的原因，这就涉及到until与before的区别问题。

实际上，只要我们把握住两者使用时本身的含义及主句动词是终止性的，还是延续性的，肯定式，还是否定式两大点，就能容易地解决这类问题。现详细阐明如下：

一、在下列情况下，两者可互换用，但含义略有不同

before表示“在……之前”的意思，强调时间先后关系;而until表示“直到……才”的意思，主句是肯定句则表示主句动作的终止时间;主句是否定句则强调主句动作的起始时间。

1.主句为否定式终止性谓语动词。常见的动词是open,start,leave,arrive,finish, stop等。例如：

(1)The noise of the street didn't stop until/before it was midnight.

(2)The children won't come back until/before it is dark.

(3)I didn't leave the lovely boy until/before his mother came home.

2.主句为肯定式、延续性谓语词，这类动词用stand,stay,talk,be,wait等。例如：

(1)He lived with his parents until/before he graduated from school.

(2)I will wait until/before he comes to my help.

(3)I shall stay heer until/before you come back.

二、在下列情况下，用before不用until

1.主句这肯定式、终止性谓语动词，只用before。例：

(1)He fell asleep before I could take off his clothes.

(2)We arrived there before it atarted to rain.

(3)The holiday came to the end befor I knew it.

(4)He almost knocked me down before he saw me.

2.主句谓语动词强调动词的迟缓性，只用before，常伴有时间段状语或时间段暗示。例：

(1)It was quite some time before he found the elephant at all.

(2)We had walked a long way before we found some water.

(3)We had sailed for two days before we saw the land.

(4)The fire lasted about four hours before the firefighters could

countrol it.

(5)It was midnight before my brother came home.

(6)It was three months before they met again.

3.如果强调从句谓语动作未发生，就发生主句谓语动作，只用before。常译为“未及”，“不”或“不等……就”。例：

(1)We can leave early in the morning before it gets too hot.

(2)I must write it down before I forget it.

(3)We do want to buy something now before prices go up.

4.表“与其说……倒不如”，“与其……毋宁……”只用before。例：

(1)I would give up my job before I'd agree to be dismissed.

(2)He will die of hunger before he will steal.

5.在某些特定句型中用before。例如：

(1)It was not long before the whole country rose up.

(2)It will probably not be long before they understand each other.

三、下列情况一般区别用until

1.主句是持续性谓语动词时，肯定、否定都可以，但意义完全不同。肯定表动作终止，而否定表动作开始。例如：

(1)We discussed the problem until/before he came back.我们一直讨论到他回 来。

(2)We didn't discuss the problem until he came back.我们一直等到他回来后才讨论问题。

2.not…until句型尽管在某些情况下可与before互换用，但在强调句中一般仍用until。

例如：

(1)It was not until he told me that I knew it.

(2)It was not until he finished his homework that he went home.

综上所述，前面的4条选择题中，第1、3题强调动作发生的迟缓性应选before。第2题表动作未及发生就发生主句动作也应选before。第4题为强调句应选A项。

(五)其他时间状语从句的用法

1.由since引导的时间状语从句。

since引导的从句的谓语动词可以是延续性的动词，又可以是瞬时动词。一般情况下，从句谓语动词用一般过去时，而主句的谓语动词用现在完成时。但在It is +时间+since从句的句型中，主句多用一般现在时。例如：

I have been in Beijing since you left. 自从你离开以来，我一直在北京了。

Where have you been since I last saw you? 自上次我和你见面以后，你到哪里去了?

It is four years since my sister lived in Beijing. 我妹妹不在北京住有四年了。

It is five months since our boss was in Beijing.我们老板离开北京有五个月了。

知识扩展

1. It is since从。。。以来多长时间了(因为since +从句或名词，表示一段时间)

It is five years since we met last time.从我们上次见面已经五年了。

2. It is +before…(。。。才)It was a long time before I went to sleep again.过了很长时间我才睡着。It was an hour before(=until) the police arrived.过了一个小时，警察才来。

3.由as soon as, immediately, directly, instantly, the moment, the instant, the minute, 等引导的时间状语从句。这些连词都表示“一……就”。

例如：I will go there directly I have finished my breakfast. 吃完早饭，我立即到那里去。

The moment I heard the news, I hastened to the spot.我一听到消息，马上赶到了出事地点。

As soon as I reach Canada, I will ring you up. 我一到加拿大，就给你来电话。

4.由by the time引导的时间状语从句。注意时态的变化：在一般情况下，如果从句的谓语动词用一般过去时，主句的谓语动词用过去完成时;如果主句的谓语动词用一般现在时，主句的谓语动词用将来完成时。

例如：By the time you came back, I had finished this book.到你回来时，我已经写完这本书了。

By the time you come here tomorrow, I will have finished this work. 你明天来这儿的时候，我将已经完成此工作了。

注意：when while as after before as soon as since till /until by the time 在时间状语从句中，要注意时态一致。一般情况下主句是将来时的时候，从句要用一般现在时。

六、练习：在下列各句的空格中填入适当的连词

1._____ he comes tomorrow, I shall ask where he has been.

2._____ he was speaking, everybody listened carefully.

3.I saw her just _____she was getting off the train.

4.Have a good look at that man _____you pass him.

5.It was already eight o'clock _____we got there.

6. I was about to go out _____ a visitor came.

7.We'll go to the country at the beginning of June, ____ the summer harvest will start.

8. He learned to speak German _____ he was in Berlin.

9. Henry is in charge of the office _____ Mr. Smith is away.

10. I listen to the recorder ______ I have time.

11. He had learned Chinese ______he came to China.

12. _____ the work was done, we sat down to sum up experience.

13. I haven't seen him _____he moved to the other side of the town.

14. I waited _____ he came back.

15. It was not _____ he took off his eyeglasses that I recognized him.

16. She likes everything to be in place _____ she starts to work.

17. The thieves ran away ______they caught sight of the police.

18. They decided to go back home ______ their money ran out.

19. We played outside till sunset, ______it began to rain。

20. _______ I get to the airport, I will phone you to pick me up.

21. They were about to leave _____ it began to rain.

22. He always stay in bed _____ lunch time.

23. I like playing tennis _______my younger sister prefers watching ball games.

24. ______ I understand your viewpoint, I don’t agree with you.

25. ______ she grew older, she became more responsible.

二、从A、B、C、D中选出可以填入空白处的最佳答案。

1. It was quiet _____those big trucks started coming through the town.

A. before B. after C. until D. unless

2. It seemed only seconds _____ the boy finished washing his face.

A. when B. before C. after D. even if

3. Hardly had he reached the school gate _____ the bell rang.

A. while B. when C. as D. as soon as

4. ______you begin, I think you must continue.

A. When B. Whenever C. Once D. Even if

5. I remembered you ______ I saw you at the airport.

A. the moment B. while C. after D. once

6. He was about to go to bed ______ the doorbell rang.

A. while B. as C. before D. when

7.______I listen to your advice, I get into trouble.

A. Every time B. When C. While D. Until

8. _____ John was watching TV, his wife was cooking.

A. As B. As soon as C. While D. Till

9. The children ran away from the orchard(果园) ______ they saw the guard.

A. the moment B. after C. before D. as

Key:

1. When 　2. While / When 　3. as 　4. when/as　5. when

6. when 7. when 8. while　9. while　10. whenever　11. before

12. After 13. since 　14. till/until　15. until 　16. before

17. as soon as 　18. before 19. when　20. As soon as　21.when

22. until 　23. while　24. While 25. As

二、1. C 2. B 3. B 4. C 5. A 6. D 7.A 8.C 9.A

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