情态动词+have done的用法x09could+have done：本可以做而实际上未能做.x09You could have done better, but you didn’t try your best.
x09cannot+ have done：表示对现在或过去行为的否定推测.x09He cannot have been to that town.
x09can+主语+ have done：表示对过去行为的怀疑或不肯定（用在疑问句中）.x09Can he have got the book?
x09might(may)+ have done：对过去发生的行为不太肯定的推测.x09He may not have finished the work.
If we had taken the other road, we might have arrived earlier.
x09must+ have done：对过去发生的行为肯定的推测.
其否定式为：cannot have done.x09You must have seen the film.
You cannot have seen the film.
x09needn’t+ have done：本来不必要做的而实际上又做了.x09You 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.
x09should(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.x09You 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x09用 法x09例 句
If引导的
条件从句x09与现在事实相反x09从句动词：过去式（be用were）
主句动词：should/would/could/might+dox09If he were here, he would help us.
x09与过去事实相反x09从句动词：had+done
主句动词：should/would/could/might+have+donex09If I had been free,I would have visited you.
x09与将来事实相反x09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x09If it should rain tomorrow, we would not go camping.
省略if的虚拟条件句x09将虚拟条件从句中的were,had,should放到主语之前,构成主谓倒装x09①Should 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x09不同时间的虚拟：各遵守各的规则x09①If 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.
x09虚拟与陈述的混合：各遵守各的规则x09①He 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x09but for+名词表示虚拟条件x09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.x09---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
x09without+名词表示虚拟条件x09x09Without the air to hold some of the sun's heat, the earth at night would be freezing cold.
x09动词不定式表示虚拟条件x09x09It would be only partly right to follow in this way.
如果用这种方式,仅仅对了一半.
x09现在分词表示虚拟条件x09x09Having 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.
x09过去分词表示虚拟条件x09x09Given 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.
x09副词otherwise表示虚拟条件x09x09I 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.
x09连词but连接的句子表示虚拟条件x09x09He _____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x09as 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.x09①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.
x09in order that/so that引导的状语从句中动词用can/could/may/ might/ would等+dox09Turn on the light so that we can see it clearly.
宾语从句x09demand, suggest, order, insist后接的从句中动词为should+dox09He suggested that we not change our mind.
x09wish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x09I wish I could be a pop singer.
I wish I would have gone to Shanghai last month.
主语从句x09在It is necessary / important / strange that…
It is suggested / demanded/ ordered / requested that…等从句中,
谓语动词用should+dox09It is strange that such a person should be our friends.
其它
句型中x09It is time that…句型中动词用过去式或should+dox09It’s high time that we left/should leave.
x09would rather所接的从句中动词用过去式或者过去完成式x09I would rather you stayed at home now.
x09If 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x09If only our dream had come true!