as when while 自我归纳

但属下列情形时,只用as, 而不用when或while。

A) 用于表示同一个人的两种动作交替进行, 指"一边……,一边……"。如:

The girl dances as she sings on the stage.

He looked behind from time to time as he went forward.

B)表示两个同步发展的动作或行为,译为"随着……"。如:

As time went on / by, she became more and more worried.

As children get older, they become more and more interested in the things around them.

C)表示两个短促行为或事件几乎同时发生。如:

I thought of it just as you opened your mouth.

Just as the flying worm hit her face, she gave a loud cry.

D) 后接名词表示某一年龄段时,用as。如:

As a young man, he was active in sports.

as还可以用来表示两个相互伴随着发展或变化的状态。如：

As spring warms the earth, all trees turn green. 春暖大地，绿上枝头。

当谈到两个短暂动作在同一时间发生时，常使用as或just as。当然也可以使用when。如：I thought of it just as you opened your mouth. 你刚开口，我就想起了这事。

--------------------------------------------------------------------------------------------------------------------- while表达的是一段时间而不是时间点，因此习惯用来引导过去进行时态背景的时间状语从句。如：

She entered the room while I was watching TV. 她进来时我在看电视。

常用while来表达两个动作或状态在同一时段内发生或存在，而且延续的时间比较长，有相互对比含义。在这种对比中，一般过去时和过去进行时都可以使用。as和when一般不这样使用。如：

While I was reading, she was playing. 我在读书，而她在玩耍。

从句的谓语动词如表示状态时，通常用while。如：

We must strike while the iron is hot.我们应该趁热打铁。

while和when都可以用作并列连词。

Mike is tall while his brother is short. 迈克的个子很高，然而他弟弟很矮。

Mary was on her way home when two big boys stopped her.

玛丽正走在回家的路上，这时两个大个子男孩拦住她。

①when意为"在……时刻或时期"，它可兼指"时间点"与"时间段"，所引导的从句的动词既可以是终止性动词，也可是持续性动词。如：

When I got home, he was having supper.我到家时，他正在吃饭。

When I was young, I liked dancing.我年轻时喜欢跳舞。

②while只指"时间段"，不指"时间点"，从句的动词只限于持续性动词。如：

While I slept, a thief broke in.在我睡觉时,盗贼闯了进来。

辨析

①when从句与主句动作先后发生时，不能与while互换。如：

When he has finished his work, he takes a short rest.每当他做完工作后，总要稍稍休息一下。(when = after)

When I got to the cinema, the film had already begun.当我到电影院时，电影已经开始了。(when=before)

②when从句动词为终止性动词时，不能由while替换。如：

When he came yesterday, we were playing basketball.昨天他来时，我们正在打篮球。

③当从句的谓语是表动作的延续性动词时，when, while才有可能互相替代。如：

While / When we were still laughing, the teacher came in.正当我们仍在大声嬉笑时，老师进来了。

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1.表示条件，相当于if ，意为“如果，要是”. 引导条件状语从句。

How can I get a job when I can't even read or write？

如果我连读和写都不会，我怎么能找到工作呢？

You shall have the apple when you say “Please”.你要是说“请”，这苹果就是你的。

He will likely recover when he undergoes the operation.如果动手术的话，他可能会复元。

When he receives the letter, he’ll tell us.他要是收到信就会告诉我们的。

I’ll do that when necessary.有必要我就会那样做。

How can you hope for mercy yourself when you show none?

如果你不宽恕别人，你自己怎能希望得到别人的宽恕呢？

2.when 分句前面的分句使用was（were）about to，was（were）on the point 等。

引导并列分句总是置于另一分句之后，不可前置，相当于and just at the time。

We were about to start when it began to rain. 我们刚要出发就开始下雨了。

He was on the point of leaving when someone knocked at the door. 他刚要走就有人敲门。

I was just about to go swimming when luckily our guide saw me and shouted at me.

我正要去游泳，这时我们的导游看见我并对着我喊叫。

We were watching TV, when suddenly the light went out.我们正在看电视，灯突然熄了。

3.表示对比，主要有以下两种情况：

A. 相当于whereas，while，since，意为“既然；然而”。

1）How can I help them to understand when they won't listen to me？

既然他们不愿听我的，我又怎么能帮助他们弄明白呢？

2）They have only three copies when we need five. 他们只有三本，而我们却需要五本。

B. when 从句中使用虚拟语气，意为“本来……却……”。

1）She paid when she could have entered free. 本来可以免费入场，而她却付了款。

2）She stopped trying when she might have succeeded next time. 她本来下次有可能获得成功，但她却不再尝试了。3）They were gossiping, when they should have been working. 他们本该工作，却在那里说别人的闲话。