08 情态动词和虚拟语气
I.情态动词基本用法
情态动词 用 法 否定式 疑问式 简答式
can 能力（体力，智力，技能） 允许或许可（口语中常用） 可能性（表猜测，用于否定句或疑问句中） can not / cannot /can’t do Can…do… Yes,…can. No,…can’t.
could couldn’t do
may 可以（问句中表示请求） 可能，或许（表推测） 祝愿（用于倒装句中） may not do May…do… Yes,…may. No,…mustn’t/can’t.
might might not do Might…do… Yes,…might No,…might not.
must 必须，应该（表主观要求） 肯定，想必（肯定句中表推测） must not/mustn’t do Must…do… to. Yes,…must. No,…needn’t/don’t have
have to 只好，不得不（客观的必须，有时态和人称的变化） don’t have to do Do…have to do… Yes,…do. No,…don’t.
ought to 应当（表示义务责任，口语中多用should） ought not to/oughtn’t to do Ought…to do… Yes,…ought. No,…oughtn’t.
shall 用于一三人称征求对方意见 用于二三人称表示许诺、命令、警告、威胁等 shall not/shan’t do Shall…do… Yes,…shall. No,…shan’t.
should 应当，应该（表义务责任） 本该（含有责备意味） should not/shouldn’t do Should…do…
will 意愿，决心 请求，建议，用在问句中would比较委婉 will not/won’t do Will/Would…do… Yes,…will. No,…won’t.
would would not/wouldn’t do
dare 敢（常用于否定句和疑问句中） dare not/daren’t do Dare…do… Yes,…dare. No,…daren’t.
need 需要,必须（常用于否定句和疑问句中） need not/needn’t do Need…do… Yes,…must. No,…needn’t.
used to 过去常常（现在已不再） used not/usedn’t/usen’t to do didn’t use to do Used…to do… Did…use to do… Yes,…used. No,…use(d)n’t. Yes,…did. No,…didn’t.
II.情态动词的重点知识
表示“能力、许可”的can和 表示能力的情态动词用can/could A computer_____think for itself; it must be told what to do. A.can’t B.mustn’t C.may not D.might not
may
表示许可时用may/might ,can/could 都可以，但在问句中用could… 或might…？ 以使口气委婉客气，其回答一定要用can或may，以使回答口气明确（must表示一定，必须，mustn’t表示禁止，不许可）。 ①—Could I call you by your first name —Yes, you______ A.will B.could C.may D.might ②Johnny, you_____play with the knife, you_____hurt yourself. A.won’t/can’t B.mustn’t/may C.shouldn’t/must D.can’t/shouldn’t
在肯定句中could不可以用来表示过去某一特定场合的能力，而要用was/were able to。 The fire spread through the hotel very quickly but everyone_____get out. A.had to B.would C.could D.was able to
表示“推断、判断”的can may,must 在肯定句中都可以用来表示可能。在含义上must语气最肯定,may表示的是事实上的可能性。 Peter______come with us tonight, but he isn’t very sure yet. A.must B.may C.can D.will 而can表示的是逻辑上的可能性： 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
need need作为情态动词只有一种形式，只用于否定句和疑问句。
dare dare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）
易混知识：
易混1 对情态动词表示推测的误用
高考对情态动词表示推测的考查集中在must，may， might， can， could的用法上。
must用于肯定的陈述句中，表示肯定的推测，语气最强；may，might用于肯定和否定的陈述句中，表示可能性不大的推测，语气较弱；can用于肯定的陈述句中，表示对客观可能性的推测；can，could 用于否定的陈述句和疑问句中，表推测，语气比may／might强。
We may go to the cinema tonight, but we are not sure yet.今晚我们可能去看电影，但还没确定。（可能性不大的推测）
Accidents can happen on such rainy days.
在这样多雨的日子可能会发生事故。（对客观可能性的推测）
She can't have left school, for her bike is still here.她不可能离开学校了，因为她的自行车还在这里。（对过去的推测，语气强）
易混2 不同句式或不同时间的虚拟语气的混淆情态动词表虚拟是英语语法中的一个难点，
不同句式及不同时间的表达形式不尽相同，所以在平时学习中要熟记不同句式的虚拟形式。做题时，根据题干中的时间信息，正确判断句子表示与何时的事实相反，从而作出正确的选择。
He would lose weight， but he eats too much.他本来要减肥的，但是他吃得太多了。（根据he eats too much 可知是对现在的虚拟，根据对现在虚拟的形式可知，第一个分句谓语用“would＋动词原形”）
I would rather you had seen the film yesterday.我倒希望你昨天就看了这部电影。（由yesterday 以及 would rather后的从句用虚拟语气可知，从句谓语用“had＋过去分词”，表示对过去的虚拟）
The workers' requirement was that their working conditions be improved.工人们的要求是他们的工作条件要得到改善。（requirement后的表语从句中谓语应用“should＋动词原形”，should可以省略）
III.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+do It 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 our dream had come true!
特别注意：
（1）在if引导的虚拟条件状语从句中，谓语动词含有had，were，should时，可以把if省略，将had，were，should提到句首，变为倒装句。
Had you (=If you had) come earlier, you would have caught the early bus.如果你早点来，就能赶上早班车了。
Were I you were you), I would try it again.如果我是你，我会再试一试。
Should he come should come),tell him to ring me up.他要是来了，让他给我打个电话。
（2）当条件状语从句和主句表示的动作或行为所发生的时间不一致时，该条件句就被称为“错综时间条件句”，动词的形式要根据它所表示的时间作出相应的调整。
If you had followed the doctor's advice, you would be better now.如果你当时遵循医生的建议的话，你现在就会好多了。
（3）有时假设的条件不通过条件状语从句表达出来，而是隐含在某些词或短语中，或隐含在上下文中，这叫“含蓄条件句”。常用的这类词或短语有：
without（要是）没有 in case 如果，假使
but for要不是 for fear that 唯恐
otherwise 否则 or 否则
I couldn't have gone through that bitter period without your generous help.
如果没有你慷慨相助的话，我不可能熬过那段艰苦的日子。
We lost our way in that small village, otherwise we would have visited more places of interest yesterday.
我们在那个小村庄迷路了，要不然昨天我们就能参观更多的名胜了。
巩固练习：
单句填空
1._________you make so much noise, Jimmy Your little sister is still sleeping.
2.Using supercomputer, many labs are now conducting experiments that couldn't__________ (be)possible in the past.
3.At the routine office meeting, the headmaster insisted the problems referred to ________(pay)special attention to.
4.I wish I_________(attend) the meeting yesterday so that I didn't have to make it up later.
5.He talked about the Eiffel Tower as if he___________ (see) it for himself.
6.The firefighters failed to save the dog's owner because if they_________(walk) onto the mud,they would have sunk,too.
7.Children must_____________(teach) how to deal with dangerous situations.
8.If I____________(be) at home in Cambodia, I would have to go outdoors.
9.I am sorry I am very busy now.If I ____________(have) time,I would certainly go to the movies with you.
10.According to the local law, no one ____________enter the building site without permission.
语法填空：
Keeping a diary in English is an 1________(effect) way to improve our English writing abilities. 2 ___________(compare) with other forms of writing, it is shorter and takes less time. It can help us to develop the habit of thinking in English.If we persist in this practice, 3________(gradual) we will learn how to express ourselves in English. In keeping a diary in English, we certainly run up against many difficulties.In the first place, 4___________ happens that we have trouble 5_________ (express) our minds with appropriate words and phrases. Second,there exist Chinese idiomatic 6____________(phrase) but it is extremely hard for us to put them in English properly.
My suggestion is that a notebook 7__________ (keep)and a Chinese-English dictionary be 8________ our reach.Whenever something beats us, we can first put it down in our notebook 9__________ consult our dictionary then. In short, I firmly believe that keeping a diary 10_________ (contribute) a lot to the development of our writing skills.
解析：
单句填空：
Must句意为：吉米，你非要弄出这么大的噪音吗？你妹妹还在睡觉。由语境可知，此处表示说话人的不满，must意为“偏要，非要......不可”，符合语境。故填Must。
have been 句意为：许多实验室现在使用超级计算机进行过去不可能实现的实验。根据句意可知，此处couldn’t表示推测，意为“不可能”。再根据时间状语in the past可知，此处表示“过去不可能”，应该用couldn’t have done，故填have been。
（should） be paid 句意为：在办公室例行会议上，校长坚持要特别注意提到的问题。insist意为“坚持要求”时，其引导的宾语从句应用虚拟语气（should）do。且宾语从句的主语the problems 和pay是被动关系，故填（should）be paid。
had attended 句意为：我希望我昨天参加了会议，这样我就不必再补上（会议内容）了。wish后的宾语从句要用虚拟语气。再根据时间状语yesterday可知，此处是对过去情况的虚拟，故填had attended。
had seen 句意为：他谈起埃菲尔铁塔，就好像他亲眼见过似的。as if引导的状语从句表述不真实的或极少有可能发生或存在的情况时，应用虚拟语气。根据talked 可知，此处表示与过去事实相反，故填had seen。
had walked 句意为：消防队员未能救出狗的主人，因为如果他们踏上淤泥的话，他们也会沉下去。此处是if 引导的非真实条件句，应用虚拟语气；与过去的事实相反，从句应用过去完成时，故填had walked。
be taught 句意为：孩子们必须被教会如何处理危险的情况。从句主语 Children 和teach之间为被动关系，应用被动语态，且设空处位于情态动词must后，应用“be+去分词”形式，故填be taught。
were 句意为：如果我在柬埔寨的家里，我就不得不出门。根据主句的谓语 would have to go可知，此处是非真实条件句，与现在的事实相反，从句用一般过去时，be动词一般用were，故填were。
had 句意为：对不起，我现在太忙了。如果有时间我肯定会和你一起去看电影。本句中If引导的从句表示对现在的情况进行假设，主句用“would＋动词原形”，从句用一般过去时，故填had。
shall 句意为：根据当地法律，未经许可任何人不得进入这个建筑工地。根据law可知，此处应用shall陈述法律、规定等，意为“必须”。故填shall。
语法填空：
1．effective 句意为：用英语写日记是提高我们的英语写作能力的有效方法。此处应用形容词来修饰名词way。故填effective。
2．Compared 句意为：与其他的写作形式相比，它篇幅更短，耗时更少。分析句子结构可知，设空处应用非谓语形式，it与compare之间是逻辑上的被动关系，所以用过去分词作状语。故填Compared。
3．gradually 句意为：如果我们坚持这样做，渐渐地，我们将学会如何用英语表达自己。此处表示“逐渐地”，应用副词作状语，修饰整个主句。故填gradually。
4．it 句意为：首先，我们会有难以用合适的词语来表达我们想法的情况发生。it happens that...是固定句型，意为“会发生······情况；碰巧”，it是形式主语，that引导的从句是真正的主语。故填it。
5．expressing 句意见上一题解析。have trouble（in）doing sth.意为“做某事有困难”，是固定搭配。故填expressing。
6.phrases 句意为：第二，汉语中存在一些惯用语，但是我们很难把它们准确地翻译成英语。由复数形式的谓语动词exist和语境可知，此处应用名词复数形式，故填phrases。
7．be kept 句意为：我的建议是记笔记并在手边放一本汉英词典。suggestion 意为“提议，建议”，其后接that从句（表语从句或同位语从句）时，从句用虚拟语气（“should＋动词原形”，其中should可省略）。notebook和keep之间是被动关系，故填be kept。
8．within 句意见上一题解析。within one＇s reach 意为“伸手可及的”，为固定表达，故填介词within。
9．and 句意为：每当我们遇到困难时，我们可以先把它记在笔记本上，然后查词典。consult和 put it down并列，故填连词and。
10．contributes 句意为：总之，我坚信写日记对我们写作技能的提升有很大的帮助。that后的宾语从句中，主语为动名词短语，表单数含义，谓语动词用第三人称单数形式，此处描述客观事实，从句应用一般现在时，故填contributes。08 情态动词和虚拟语气
I.情态动词基本用法
情态动词 用 法 否定式 疑问式 简答式
can 能力（体力，智力，技能） 允许或许可（口语中常用） 可能性（表猜测，用于否定句或疑问句中） can not / cannot /can’t do Can…do… Yes,…can. No,…can’t.
could couldn’t do
may 可以（问句中表示请求） 可能，或许（表推测） 祝愿（用于倒装句中） may not do May…do… Yes,…may. No,…mustn’t/can’t.
might might not do Might…do… Yes,…might No,…might not.
must 必须，应该（表主观要求） 肯定，想必（肯定句中表推测） must not/mustn’t do Must…do… to. Yes,…must. No,…needn’t/don’t have
have to 只好，不得不（客观的必须，有时态和人称的变化） don’t have to do Do…have to do… Yes,…do. No,…don’t.
ought to 应当（表示义务责任，口语中多用should） ought not to/oughtn’t to do Ought…to do… Yes,…ought. No,…oughtn’t.
shall 用于一三人称征求对方意见 用于二三人称表示许诺、命令、警告、威胁等 shall not/shan’t do Shall…do… Yes,…shall. No,…shan’t.
should 应当，应该（表义务责任） 本该（含有责备意味） should not/shouldn’t do Should…do…
will 意愿，决心 请求，建议，用在问句中would比较委婉 will not/won’t do Will/Would…do… Yes,…will. No,…won’t.
would would not/wouldn’t do
dare 敢（常用于否定句和疑问句中） dare not/daren’t do Dare…do… Yes,…dare. No,…daren’t.
need 需要,必须（常用于否定句和疑问句中） need not/needn’t do Need…do… Yes,…must. No,…needn’t.
used to 过去常常（现在已不再） used not/usedn’t/usen’t to do didn’t use to do Used…to do… Did…use to do… Yes,…used. No,…use(d)n’t. Yes,…did. No,…didn’t.
II.情态动词的重点知识
表示“能力、许可”的can和 表示能力的情态动词用can/could A computer_____think for itself; it must be told what to do. A.can’t B.mustn’t C.may not D.might not
may
表示许可时用may/might ,can/could 都可以，但在问句中用could… 或might…？ 以使口气委婉客气，其回答一定要用can或may，以使回答口气明确（must表示一定，必须，mustn’t表示禁止，不许可）。 ①—Could I call you by your first name —Yes, you______ A.will B.could C.may D.might ②Johnny, you_____play with the knife, you_____hurt yourself. A.won’t/can’t B.mustn’t/may C.shouldn’t/must D.can’t/shouldn’t
在肯定句中could不可以用来表示过去某一特定场合的能力，而要用was/were able to。 The fire spread through the hotel very quickly but everyone_____get out. A.had to B.would C.could D.was able to
表示“推断、判断”的can may,must 在肯定句中都可以用来表示可能。在含义上must语气最肯定,may表示的是事实上的可能性。 Peter______come with us tonight, but he isn’t very sure yet. A.must B.may C.can D.will 而can表示的是逻辑上的可能性： 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
need need作为情态动词只有一种形式，只用于否定句和疑问句。
dare dare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）
易混知识：
易混1 对情态动词表示推测的误用
高考对情态动词表示推测的考查集中在must，may， might， can， could的用法上。
must用于肯定的陈述句中，表示肯定的推测，语气最强；may，might用于肯定和否定的陈述句中，表示可能性不大的推测，语气较弱；can用于肯定的陈述句中，表示对客观可能性的推测；can，could 用于否定的陈述句和疑问句中，表推测，语气比may／might强。
We may go to the cinema tonight, but we are not sure yet.今晚我们可能去看电影，但还没确定。（可能性不大的推测）
Accidents can happen on such rainy days.
在这样多雨的日子可能会发生事故。（对客观可能性的推测）
She can't have left school, for her bike is still here.她不可能离开学校了，因为她的自行车还在这里。（对过去的推测，语气强）
易混2 不同句式或不同时间的虚拟语气的混淆情态动词表虚拟是英语语法中的一个难点，
不同句式及不同时间的表达形式不尽相同，所以在平时学习中要熟记不同句式的虚拟形式。做题时，根据题干中的时间信息，正确判断句子表示与何时的事实相反，从而作出正确的选择。
He would lose weight， but he eats too much.他本来要减肥的，但是他吃得太多了。（根据he eats too much 可知是对现在的虚拟，根据对现在虚拟的形式可知，第一个分句谓语用“would＋动词原形”）
I would rather you had seen the film yesterday.我倒希望你昨天就看了这部电影。（由yesterday 以及 would rather后的从句用虚拟语气可知，从句谓语用“had＋过去分词”，表示对过去的虚拟）
The workers' requirement was that their working conditions be improved.工人们的要求是他们的工作条件要得到改善。（requirement后的表语从句中谓语应用“should＋动词原形”，should可以省略）
III.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+do It 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 our dream had come true!
特别注意：
（1）在if引导的虚拟条件状语从句中，谓语动词含有had，were，should时，可以把if省略，将had，were，should提到句首，变为倒装句。
Had you (=If you had) come earlier, you would have caught the early bus.如果你早点来，就能赶上早班车了。
Were I you were you), I would try it again.如果我是你，我会再试一试。
Should he come should come),tell him to ring me up.他要是来了，让他给我打个电话。
（2）当条件状语从句和主句表示的动作或行为所发生的时间不一致时，该条件句就被称为“错综时间条件句”，动词的形式要根据它所表示的时间作出相应的调整。
If you had followed the doctor's advice, you would be better now.如果你当时遵循医生的建议的话，你现在就会好多了。
（3）有时假设的条件不通过条件状语从句表达出来，而是隐含在某些词或短语中，或隐含在上下文中，这叫“含蓄条件句”。常用的这类词或短语有：
without（要是）没有 in case 如果，假使
but for要不是 for fear that 唯恐
otherwise 否则 or 否则
I couldn't have gone through that bitter period without your generous help.
如果没有你慷慨相助的话，我不可能熬过那段艰苦的日子。
We lost our way in that small village, otherwise we would have visited more places of interest yesterday.
我们在那个小村庄迷路了，要不然昨天我们就能参观更多的名胜了。
巩固练习：
单句填空
1._________you make so much noise, Jimmy Your little sister is still sleeping.
2.Using supercomputer, many labs are now conducting experiments that couldn't__________ (be)possible in the past.
3.At the routine office meeting, the headmaster insisted the problems referred to ________(pay)special attention to.
4.I wish I_________(attend) the meeting yesterday so that I didn't have to make it up later.
5.He talked about the Eiffel Tower as if he___________ (see) it for himself.
6.The firefighters failed to save the dog's owner because if they_________(walk) onto the mud,they would have sunk,too.
7.Children must_____________(teach) how to deal with dangerous situations.
8.If I____________(be) at home in Cambodia, I would have to go outdoors.
9.I am sorry I am very busy now.If I ____________(have) time,I would certainly go to the movies with you.
10.According to the local law, no one ____________enter the building site without permission.
语法填空：
Keeping a diary in English is an 1________(effect) way to improve our English writing abilities. 2 ___________(compare) with other forms of writing, it is shorter and takes less time. It can help us to develop the habit of thinking in English.If we persist in this practice, 3________(gradual) we will learn how to express ourselves in English. In keeping a diary in English, we certainly run up against many difficulties.In the first place, 4___________ happens that we have trouble 5_________ (express) our minds with appropriate words and phrases. Second,there exist Chinese idiomatic 6____________(phrase) but it is extremely hard for us to put them in English properly.
My suggestion is that a notebook 7__________ (keep)and a Chinese-English dictionary be 8________ our reach.Whenever something beats us, we can first put it down in our notebook 9__________ consult our dictionary then. In short, I firmly believe that keeping a diary 10_________ (contribute) a lot to the development of our writing skills.
