1) may(might) have + done sth, can (could) have + done sth　表示过去，推测过去时间里可能发生的事情。例如：

Philip may (might) have been hurt seriously in the car accident. 菲力浦可能在车祸中受了重伤。

Philip can (could) have been hurt seriously in the car accident.

2) must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。例如：

---Linda has gone to work, but her bicycle is still here. 琳达已经去上班了，但她的单车还在这儿。

---She must have gone by bus.肯定乘巴士去的。

3) ought to have done sth, should have done sth表示本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。例如：

You ought to (should) have been more careful in this experiment. 你当时在做试验时应该更仔细点。

He ought not to have thrown the old clothes away.他不该把旧衣服扔了。(事实上已扔了。)

ought to 在语气上比should 要强。

4) needn't have done sth表示本没必要做某事，但做了。例如：

I dressed very warmly for the trip, but I needn't have done so. The weather was hot.

旅行时，我衣服穿得较多，其实没有必要。那时天很热。

5) would like to have done sth表示本打算做某事，但没做。例如：

I would like to have read the article, but I was very busy then. 我想读这篇文章，但太忙了一直没读。

17.8 21.8 should 和ought to

除了上述的用法，两者还可表示"想必一定，按理应该"的意思。例如：

I ought to be able to live on my salary. 靠我的薪水，想必也能维持了。

It ought to be ready now. 想必现在准备好了吧。

They should be there by now, I think. 现在他们该到那儿了。

The poems should be out in a month at most. 诗集估计最多还有一个月就要出版了。

21.9 had better表示"最好"，相当于一个助动词，它只有一种形式，它后面要跟动词原形。例如：

It is pretty cold. You'd better put on my coat. 天相当冷。你最好穿上我的外套。

She'd better not play with the dog. 她最好不要玩耍那条狗。

had better have done sth表示与事实相反的结果，意为"本来最好"。例如：

You had better have come earlier. 你本该来得早一点。

21.10 would rather表示"宁愿"

would rather do

would rather not do

would rather… than…　 宁愿…而不愿。

还有would sooner, had rather, had sooner都表示"宁愿"、"宁可"的意思。例如：

If I have a choice, I had sooner not continue my studies at this school. 如果有选择的余地，我宁可辍学离开这个学校。

I would rather stay here than go home. = I would stay here rather than go home. 我宁愿呆在这儿，而不愿回家。

典型例题

----Shall we go skating or stay at home?

----Which ___ do?

A. do you rather　　B. would you rather　 C. will you rather　 D. should you rather

答案B。本题考查情态动词rather的用法，would rather +do sth 意为"宁愿"，本题为疑问句，would 提前，所以选B。

21.11 will和would

注意：1)would like;would like to do = want to 想要，为固定搭配。例如：

Would you like to go with me? 想和我一块去吗?

2)Will you…?　Would you like…? 表示肯定含义的请求劝说时，疑问句中一般用some, 而不是any。例如：

Would you like some cake? 吃点蛋糕吧。

3)否定结构中用will，一般不用would, won't you是一种委婉语气。

Won't you sit down? 你不坐下吗?

21.12 情态动词的回答方式

问句 肯定回答 否定回答

Need you…? Yes, I must. No, I needn't

Must you…? No, I don't have to.

典型例题

1)---Could I borrow your dictionary?

---Yes, of course, you____.

A. might　B. will　 C. can　 D. should

答案C. could表示委婉的语气，并不为时态。答语中of course，表示肯定的语气，允许某人做某事时，用can和 may来表达，不能用could或might。will 与you连用，用来提出要求或下命令。should与you 连用，用来提出劝告。

2)---Shall I tell John about it?

---No, you ___. I've told him already.

A. needn't　　B. wouldn't　　C. mustn't　　D. shouldn't

答案A。needn't 不必，不用。 wouldn't 将不, 不会的。 mustn't 禁止、不能。 shouldn't　不应该。本题为不需要，不必的意思，应用needn't。

3)---Don't forget to come to my birthday party tomorrow.

---______.

A. I don't　 B.　I won't　 C. I can't　D. I haven't

答案B. will既可当作情态动词，表请求、建议、也可作为实义动词表"意愿、意志、决心"，本题表示决心，选B。

21.13 带to 的情态动词

带to 的情态动词有四个：ought to, have to, used to, be to, 如加上have got to (=must), be able to，为六个。它们的疑问、否定形式应予以注意：

Do they have to pay their bill before the end of the month?

She didn't use to play tennis before she was fourteen.

You ought not to have told her all about it.

Ought he to see a heart specialist at once.?

ought to 本身作为情态动词使用。其他的词作为实义动词使用，变疑问，否定时，须有do 等助动词协助。

典型例题

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

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

答案A。由于后句为过去时，告诉秘密的动作又发生在其前因，此地应用过去完成时，但它在情态动词 ought to 后，所以用have told。

21.14 比较need和dare

这两词既可做实义动词用，又可做情态动词用。作为情态动词，两者都只能用于疑问句，否定句和条件句。need 作实义动词时后面的不定式必须带to，而dare作实义动词用时, 后面的to 时常可以被省略。

1) 实义动词：need(需要, 要求) need + n. / to do sth

2) 情态动词：need，只用原形need后加do，否定形式为need not。例如：

Need you go yet? 你要走了吗?

Yes, I must. / No, I needn't.是的，我要走了/不，不急着走。

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