Mary is in poor health. She can be ill at any times.

在否定句中只能用can和may。所以can’t时用以代替mustn’t，语气比may更肯定。中文可以翻译为不可能。Michael______be a policeman, for he’s much too short.

A.needn’t B.can’t C.should D.may

在疑问句只能用can，不能用may和must。He may be very busy now. Can he be very busy now?

He must be very busy now. Can he be very busy now?

needneed作为情态动词只有一种形式，只用于否定句和疑问句。

daredare作为情态动词用时有两种形式：dare和dared两个词形，除了可以用于否定句和疑问句外，还可以用于条件从句或表示怀疑的句子中。If he dare come,I will kick him out. I don’t know whether he

dare say.

注意:He doesn’t dare(to)answer the question.(否定句)

Does she dare(to)enter the dark room?(疑问句)

shall用于第一人称：征求对方的意见。What shall we do this evening?

用于第二、三人称：警告、命令、允诺、威胁等。You shall fail if you don’t work harder. 警告

He shall have the book when I finish reading.允诺

He shall be punished.威胁

should劝告、建议、命令、应该做、道义上的责任。You should(ought to) go to class right away.

I should(ought to) help him because he is in trouble.

will/would请求、建议，would比will委婉客气。Would you pass me the book?

表示意志、愿望和决心。I will never do that again.

They asked us if we would do that again

would可表示过去反复发生的动作或某种倾向。During the vacation he would visit me every week

The wound would not heal.(伤口老是不能愈合)

would表示估计或猜想。It would be about ten when he left home.

What would she be doing there?

情态动词+have done的用法could+have done：本可以做而实际上未能做。You could have done better, but you didn’t try your best.

cannot+ have done：表示对现在或过去行为的否定推测。He cannot have been to that town.

can+主语+ have done：表示对过去行为的怀疑或不肯定(用在疑问句中)。Can he have got the book?

might(may)+ have done：对过去发生的行为不太肯定的推测。He may not have finished the work.

If we had taken the other road, we might have arrived earlier.

must+ have done：对过去发生的行为肯定的推测。

其否定式为：cannot have done。You must have seen the film.

You cannot have seen the film.

needn’t+ have done：本来不必要做的而实际上又做了。You needn’t have watered the flowers,for it is going to rain.

注意：didn’t need to(have to)do：

没有必要做而实际上也没有做

I didn’t need to clean the windows.My sister did it 2 hours ago.

should(ought to)+ have done：本来应该做而实际上又没有做。其否定形式表示某中行为不该发生却发生了。You should have started earlier, but you didn’t.

She shouldn’t have taken away my measuring tape,

for I worked to use it.

注意：He should have finished the work by now.(表推测)

虚拟语气

类 别 用 法 例 句

If引导的

条件从句 与现在事实相反 从句动词：过去式(be用were)

主句动词：should/would/could/might+do If he were here, he would help us.

与过去事实相反 从句动词：had+done

主句动词：should/would/could/might+have+done If I had been free,I would have visited you.

与将来事实相反 从句动词：过去式/should+动词原形/were+to do

主句动词：should/would/could/might+动词原形 If it should rain tomorrow, we would not go camping.

省略if的虚拟条件句 将虚拟条件从句中的were，had,should放到主语之前，构成主谓倒装 ①Should he come ,tell him to ring me up.

②Were I you,I would not do it.

③Had I been free,I would have visited you.

混合虚拟条件句 不同时间的虚拟：各遵守各的规则 ①If he had listened to me, he would not be in trouble now.

②If he had told me yesterday,I should know what to do now.

③If I were you, I would have gone to her birthday party.

虚拟与陈述的混合：各遵守各的规则 ①He could have passed the exam,but he wasn’t careful enough.

②You should have come earlier.The bus left a moment ago.

含蓄虚拟

条件句 but for+名词表示虚拟条件 句子或主句中的谓语动词的形式视具体情况而定。这是考查考生应变能力的最佳试题。---But for your timely warning,we ______ into great trouble.

---You know we’re friends.

A. would get B. must have got

C. would have got D. can’t have got

without+名词表示虚拟条件 Without the air to hold some of the sun's heat, the earth at night would be freezing cold.

动词不定式表示虚拟条件 It would be only partly right to follow in this way.

如果用这种方式，仅仅对了一半。

现在分词表示虚拟条件 Having known in time ,we might have prevented the accident.要是及时得知的话，我们也许能阻止这场事故。

过去分词表示虚拟条件 Given more attention, the tree could have grown better.

如果多留心的话，这树本来可以长的更好。

副词otherwise表示虚拟条件 I was too busy at that time.Otherwise,I would have called you.我当时太忙，否则我就给你打电话了。

连词but连接的句子表示虚拟条件 He _____fatter but he eats too little .

A. would become B. would have become

C. must become D. must have become

其它

状语从句 as if/as though引导的状语从句中动词用did或had+done或would/could/might+do。

注意：as if/as though引导的状语从句中也可以用陈述语气：

当说话者认为所述的是真实的或极有可能发生或存在的事实时：

It sounds as if it is raining.听起来像是在下雨。

He talks as if he is drunk.从他谈话的样子来看他是醉了。①与现在事实相反

He talks as if he knew where she was.

②与过去事实相反

He talks about Rome as if he had been there before.

③与将来事实相反

He opened his mouth as if he would say something.

in order that/so that引导的状语从句中动词用can/could/may/ might/ would等+do Turn on the light so that we can see it clearly.

宾语从句 demand, suggest, order, insist后接的从句中动词为should+do He suggested that we not change our mind.

wish后的从句中分别用过去式，过去完成式和should/would+do表示与现在，过去和将来情况相反 I wish I could be a pop singer.

I wish I would have gone to Shanghai last month.

主语从句 在It is necessary / important / strange that…

It is suggested / demanded/ ordered / requested that…等从句中，

谓语动词用should+doIt is strange that such a person should be our friends.

其它

句型中 It is time that…句型中动词用过去式或should+do It’s high time that we left/should leave.

would rather所接的从句中动词用过去式或者过去完成式 I would rather you stayed at home now.

If only句型中动词常用过去式或者过去完成式，表示强烈的愿望 If only

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