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1.ought to的用法

1）ought to语气较重，有时候也会含责备之意。ought后面必须跟带to的动词不定式，否定式是ought not加带to的动词不定式。

如：He said you ought to tell the police.他说你应该去报警。

2）ought to一般可以指将来，指现在常用于进行时态，在肯定句中用完成时表示应该做但没做；在否定句中用完成时，表示不应该做的事情发生了。

如：At your age,you ought to be earning your living. 你到这个年龄应当自食其力了。

The student ought to have done his homework more carefully. 这位学生做作业时本应该更加细心。

He oughtn't to have been so late. 他本不应该来这么晚。

2.should的用法

1）should 作为情态动词,通常用来表示现在或将来的责任或义务,译作“应该”、“应当”,这时它可以和 ought to, be supposed to 互换使用。

如：You should （= ought to ） tell your mother about it at once. 你应该立刻告诉你母亲。

2）should 作为情态动词,可以用在条件状语从句中,表示语气较强的假设,译作“万一”、“竟然”,这时也可将 should 置于从句之首,即将 should 放在主语前面,而省略从属连词 if 。

如：If you should fail to come, ask Mrs Chen to work in your place. （= Should you fail to come, ask Mrs Chen to work in your place. ）如果你不能来，让陈女士来代替你。

3）should 作为情态动词,可以表示谦逊、客气、委婉之意,译为“可……”、“倒……”。

如：I should say that it would be better to try it again.我可以说再试一次会更好的。

4）should 作为情态动词,可以用来表示意外、惊喜或者在说话人看来是不可思议的.尤其在以 why, who, how 等开头的修辞疑问句或某些感叹句中常常译为“竟会”、“居然”。

如：How should I know it ? 我怎么会知道这件事?

5）should 作为情态动词,可以用来表示有较大可能实现的猜测、推论,通常译为“可能”、“总该……吧”,相当于 be expected to 。

如：They should be home by now, I think. 我想现在他们总该到家了吧.

6）should 作为情态动词,用在由 so that, for fear that, lest 引导的目的状语从句和 in case （that） 引导的条件状语从句中,有“能够”、“可能”、“会”之意。

They got up early so that they should （= could/ might） catch the first bus in time.他们起床得早以便于及时赶上早班车。

7）should 作为情态动词,可以用于下列虚拟语气句中：

用在表示与将来事实相反的条件状语从句中,构成“ If …… should （do sth）……, …… would/ could/ might （do sth.） …… ”句式

用在 suggest （propose）, arrange, plan, decide, advise, order, demand, request, desire, insist 等表示“建议”、“要求”、“命令”、“决定”、“安排”、“计划”、“主张”的动词后面接的宾语从句中.这里的 should 也可以省略.

3.would的用法

1）表示意愿

will 表示现在的意愿，would表示过去的意愿：

如：I will pay you at the rate you ask. 我愿意照你要求的价钱付款。

He wouldn’t help me yesterday. 他昨天不愿帮助我。

She asked if I would go with them. 她问我是否愿同他们一起去。

2）表示征求意见或提出请求

主要用于第二人称的疑问句中，will和would均可用，would此时并不表过去，而表示委婉语气：

Will [would] you please post the letter for me? 请帮我寄了这封信好吗?

Would Sunday night suit you? 星期天晚上适合你吗?

4.优选试题

1．I thought you like something to read，so I have brought you some books．A．may B．might C．could D．must

2．There was plenty of time．She ．

A．mustn’t have hurried B．couldn’t have hurried C．must not hurry D．needn’t have hurried

3．The plant is dead．I it more water．

A．Will give B．would have given C．must give D．should have given

4．You return the book now．You can keep it till next week if you like．

A．can’t B．mustn’t C．needn’t D．may not

5.Tom ought not to me your secret，but he meant no harm．

A．have told B．tell C．be telling D．having told

6．He you more help，even though he was very busy．

A．might have given B．might give C．may have given D．may give

7．He at the meeting this morning．He was in hospital at the time．

A．couldn’t have spoken B．mustn’t have spoken C．shouldn’t have spoken D．needn’t have spoken

8．He must be in the classroom， he?

A．mustn’t B．can’t C．isn’t D．can

9．—You were driving at 100 km an hour，sir．

—But officer，I ．My car can’t go more than 80．

A．may not have been B．couldn’t have beenC．wouldn’t have been D．needn’t have been

10．—Did you visit the famous museum?

—No．We it，but we spent too much time shopping．

A．could have visited B．must have viste C．can’t have visited D．shouldn’t have visited

11．—When can I come for the photos? I need them tomorrow afternoon．

—Theybe ready by 12：00．

A．can B．should C．might D．need

12．You to the meeting this afternoon if you have something important to do．

A．needn’t to come B．don’t need come

C．don’t need coming D．needn’t come

13．Put on more clothes．You be feeling cold with only a shirt on．

A．can B．could C．would D．must

14．—There were already five people in the car but they managed to take me as well．

—Ita comfortable journey．

A．can’t be B．shouldn’t be C．mustn’t have been D．couldn’t have been

15．I think all drivers seat belts．

A．should wear B．had better wear C．can wear D．have to wear