高中英语必修三unit2语法

need和dare的用法

1. 用作情态动词

--Need I come? --Yes, you must.

--我需要来吗？ --需要。

You needn’t telephone him now.

你现在不必打电话给他。

I don’t think you need worry.

我想你不必发愁。

She dare not go out alone at night.

她晚上不敢一个人出去。

How dare you say I’m unfair?

你竟敢说我不公平？

Not one of them dared mention this.

他们谁也不敢提这件事。



2. 用作实义动词

You don’t need to do it yourself.

你不必亲自做这件事。

We need to tell them the news.

我们需要把这消息告诉他们。

The table needs painting (to be painted.).

桌子需要油漆一下。

We should dare to give our own opinion.

我们要敢于提出自己的观点。

He did not dare (to) look up.

他不敢抬头看。

I dare day he’ll come again.

我想他会再来的。

（I dare say…为固定习语）

had better, should, ought to用法

had better, should, ought to是重要的情态动词，也是高考重要考点，学习时应注意下列几点：



一、了解相互间关系 had better(最好), should(应该)与ought to（应该）均为提建议、阐述观点的情态动词，其后接动词原形。should 比had better语气强，ought to语气最强。一般情况下should与ought to可通用。

例1：You had better go there at once.

你最好立即去那里。



例2：You ought to / should work hard.

你应该努力工作。



值得注意的是：should还有"竟然"之意，表出乎意料。



例：You can't imagine that a well-behaved gentleman should be so rude to a lady.

你真是难以想象这么一个有风度的先生对一个女子是如此之粗鲁。



二、 掌握句型变换方法 had better, should, ought to作为情态动词，各种句型变换均在自身形式上作变化。

（一）否定句

had better, should, ought to用于否定句时，否定词均位于其后，具体形式为：had better not do, shouldn't / should not do, oughtn't to do。



例1：You had better not start at this time.

此时你最好别出发。



例2：He shouldn't be careless in class.

他上课时不应粗心。



例3：She oughtn't to waste time.

她不应该浪费时间。



（二）一般疑问句

had better, should, ought to用于一般疑问句时，分别将had, should, ought提至句首。



例1：Had he better start early at once?

他最好立即出发吗？



例2：Should you do like this?

你应该这么做吗？



例3：Ought he to go there?

他应该去那里吗？



（三）反意疑问句

陈述句谓语动词含had better, should, ought to时，反意疑问句为：had, sho

uld与ought+主格人称代词或hadn't, shouldn't, oughtn't+主格人称代词。

例1：You had better not go home, had you?

你最好别回家，是吗？



例2：You should study hard, shouldn't you?

你应该认真学习，是吗？



例3：He oughtn't to speak in class, ought he?

你上课不应该讲话，是吗？



三、 掌握其完成式用法 had better没有完成式，should与ought to完成式意义与用法完全相同。

（一）should/ought to have done 意为本来应做但实际没有做，表达遗憾的感情色彩。

例：There was a lot of fun at yesterday's party. You ________ come, but why didn't you?

A. must have B. should C. need have D. ought to have

析：答案D。 该空含你本来应来但实际未来之意，应填ought to have。



（二）should / oughtn't to have done，意为本来不应做但实际已做，表达遗憾的感情色彩。

例：I was really anxious about you. You ________ home without a word.

A. mustn't leave

B. shouldn't have left

C. couldn't have left

D. needn't leave

析：答案B。 该空含你本不应该一句话不说就离开家但实际已这么做之意，所以应填shouldn't have left。





must，have to和have got to的用法

一、must的用法
　1）表示主观的义务和必要, 主要用于肯定句和疑问句, 意思为 “必须……，得……，要……”；由must引起的疑问句，肯定回答要用must或have to, 否定回答要用needn’t或don’t have to, 意思是“不必”；must的否定形式mustn’t表示禁止，意思是“不能，不许”。如：
We must find a good method to learn computer well.
我们必须找一个学好电脑的方法。
—Must I finish the task right now?
我现在必须完成这个工作吗？
—Yes, you must. / Yes, you have to. 是的。
(—No, you needn’t. / No, you don’t have to. 不，不必。)
You mustn’t come here without permission. 未经允许，你不能来这儿。
　2）表示肯定的猜测，常用于肯定句中，意思为 “一定是, 必然……”。
注意must表示推断或猜测的几种情况:
Your sister must be a doctor in this hospital. （现在的猜测）
你姐姐一定是这家医院的医生。
He must be reading newspapers in the reading room now.
（正在进行的猜测）
他此刻一定正在阅览室读报。
It must have rained last night, for the ground is wet. （过去的猜测）
昨晚一定下雨了，因为地面上是湿的。
　

二、have to / have got to 的用法
　1）must表示一种主观的需要，而have to 表示一种客观的需要，意思是“不得不”。 如：
I have to attend an important meeting this afternoon.
今天下午我不得不参加

一个重要的会议。
Mother is out, so I have to look after the shop.
妈妈不在家，因此我不得不照看商店。
　2）have to 的否定形式是don’t have to, 相当于needn’t。如：
They don’t have to buy a computer at present.
他们目前没有必要买电脑。
　3）have to 与have got to 常可以互换。