大学英语语法专题(1)

一、情态动词

1．could have done sth 表示过去可能完成却未完成的动作

e.g. Judging from what you said, he could have done this work still better.

2. cannot/could not have done sth 表示对过去情况的猜测，“不可能做过某事”。

e.g. This composition is too good; she can’t have written it hersel

f.

3. may/might as well do sth 表示建议，“还是……好”、“还不如……”

e.g. If you don’t like to swim, you may as well stay at home.

4. may/might have done sth 表示对过去事情的猜测，“可能已经……”

e.g. He may have been waiting for us for an hour.

5.mustn’t 表示禁止

don’t have to 表示不必

6.must be 表示对现在情况的推测，“一定是……”

e.g. He must be ill. He looks so pale.

7.must have done sth 表示对过去事情进行的推测，“想必一定……”

e.g. It must have been raining all the night. There are big puddles in the garden.

8.needn’t have done sth 表示过去做了不必要的事

e.g. That’s all settled. It needn’t be talked about.

9. didn’t need to do sth 表示不必做，实际上没有做

e.g. You did not need to come for the group meeting ,so we didn’t inform you.

1. If I were the President, I should/would declare November 1a national holiday.

2.One investigation showed that 40% of those killed in auto accidents could have been saved if they have been wearing seat belts.

3. If you did that again, we would n’t allow you to work with us.

注意：

1．区别if引导的真实条件句：If it doesn't rain tomorrow，we will go there by bike.(主将从现)

2. 错综时间条件句

e.g. 1)If he had got up earlier, he would not be late now.(从句说过去，主句说现在)

2)If we hadn’t been working hard in the past few years, things wouldn’t be going smoothly now.(从句说过去，主句说现在)

3.条件句中的谓语如果含有were, had, should, 从句可省略if, 同时助动词倒装至主语前。

e.g. 1) Were there no gravity(=If there were no gravity), there would be no air around the earth.

2)Should they(=If they should)have forgotten to bring a compass with them, they would have got lost in the woods.

3)Were it not for(=If it were not for)the rain, we could play football now.

4)Had it not been for(=If it hadn’t been for)your help, I would have died.

4.if only(要是……就好了，用来引导虚拟条件从句，表达强烈的愿望和遗憾)

e.g. If only I had more money, I could buy some new books.

only if(只有在……条件下，不用虚拟语气，当它至于句首时，主句要倒装)

e.g. Only if you help me can I succeed.

5.for fear that, lest, in case(以免)等引导的目的状语从句须用虚拟语气，从句中使用“should+动词原形”，should 也可省略。

e.g.1)He did not enter for fear that he(should)interfere with us.

2) Batteries are kept in dry places in case electricity(should)leak away.

若in case表示“如果、即使”，引导真实条件从句时，用陈述语气。

e.g. In case they are late, we can always sit in the bar.

6.It’s(about/high)time…sb. did sth.表示“是该……的时候了”，用一般过去式表示虚拟。

e.g. It is high time that a doctor were sent for.

三、从句

（一）名词性从句

1.主语从句

That our team is weaker is an obvious fact.(that只起连接作用)

Which plan is better is clear now.

It is strange that the children are so quiet.

注意：

Whatever(=anything that)was said here must be kept secret.

Whoever(=anyone who)doesn’t agree can come to me after the meeting.

2.表语从句

The problem is who we can get to replace her.

The truth is that he heated us.

The reason why he was late was that his bike broke down on the way to school.(当主句中的主语是reason, cause或由why引导的主语从句时，表语从句用that,而不能用because。在It/That/This is because…的句型中，可以用because。)

3.宾语从句

I don’t care whether she will come or not.

You get out of life what(=the things that)you put in.

I will give it to whoever(=anyone who)needs it.

I’m glad that you can come.(be+adj+clause)

4.同位语从句（一般跟在一些名词后面，用以说明该名词表示的具体内容，多用that引导，可以跟的名词有answer, belief, decision, evidence, fact, idea, message, news, opinion, problem, truth, thought, etc.）

I had no idea that you were here.

注意：

The news that our team won inspired all of us.(同从，that不担任从句成分)

What’s the news that upset her so much?(定从，that作主语)

（二）定语从句

引导词：关系代词who, whom, whose, which, that, as, but和关系副词when, where, why, that 1.This is the classroom where I first met him.

This is the classroom that we are to clean today.