情態(tài)動(dòng)詞和虛擬語(yǔ)氣

1、情態(tài)動(dòng)詞和虛擬語(yǔ)氣情態(tài)動(dòng)詞的用法要點(diǎn)一、 表能力CanAm/is/are able to 表現(xiàn)在的能力Will be able to 表將來(lái)的能力couldWas/were able to 表過(guò)去得能力Could have+過(guò)去分詞：表示過(guò)去有能力做但未做二、 表推測(cè)（可能性）1. 可能性可分為客觀的可能性和具體事情實(shí)際發(fā)生的可能性兩種。所謂客觀的（理論的）可能性即并不涉及具體某事是否會(huì)發(fā)生，此種用法常常可以說(shuō)明人或事物的特征。情態(tài)動(dòng)詞can可用于肯定句中表示客觀的（理論的）可能性，而表示具體事情實(shí)際發(fā)生的可能性時(shí)，can一般不用于肯定句。Accidents can happen on suc

2、h rainy days.We may go to the cinema tonight, but we are not sure yet.2. 表示具體事情實(shí)際發(fā)生的可能性：（1）表示具體事情實(shí)際發(fā)生的可能性的層次比較：詞形肯定式否定式疑問(wèn)式Must必定，必然/Will很可能，大概不會(huì)，不該會(huì).嗎Would可能性比will小語(yǔ)氣比wont弱語(yǔ)氣比will弱Should按說(shuō)應(yīng)該應(yīng)該不會(huì)Ought to 按說(shuō)應(yīng)該應(yīng)該不會(huì)Can不可能有可能嗎Could微弱的可能不可能語(yǔ)氣比can弱May 或許，也許，也未可知，也說(shuō)不定可能不might比may還弱比may not 還弱（2）表示具體事情實(shí)際發(fā)生的可

3、能性時(shí)，may, must 常用于肯定句，一般不用于否定句和疑問(wèn)句（may not 表示“可能不”）；can常用于否定句、疑問(wèn)句或感嘆句中，表示疑惑、驚訝或不相信等意思；could既可用于肯定句又可用于否定句、疑問(wèn)句中。This cant/ couldnt be done by him.This may not be done by him.He could be on his way home now.Can this be done by him?Mr Mush is on time for everything. How can it be that he was late for th

4、e opening ceremony?I didnt hear the phone. I must have been asleep.-Are you coming to Jeffparty?-Im not sure. I might go to the concert instead.(3) would, could, should, might 并不一定與過(guò)去時(shí)間有關(guān)，而表示可能性弱于它們相應(yīng)的現(xiàn)在時(shí)形式。This may/ might be done by him.(4)should 表推測(cè)時(shí)，表示確定或可能有的未來(lái)或期望，即合乎理想的情況或結(jié)果He ought to/ should b

5、e here on time-he started early enough.We should arrive before dark.The roads should be less crowded today.三、 表示請(qǐng)求、允許、允諾1. 當(dāng)對(duì)方是決策者時(shí)，你代表你（們）自己（I, we），或代表第三者（he she they）向?qū)Ψ剑▂ou）請(qǐng)示或提出建議時(shí)用：（1） Shall/ May/ Might/ Can/ Could I/ we?（2） Shall he/ she/ they.?（3） Would/ Will you?Shall the driver wait outside

6、?When shall my father be able to leave hospital?Would you do me a favor?2. could/ might/ would/ should表委婉的語(yǔ)氣-Could/ Might I use your bike tomorrow morning?-Yes, you can/ may.3. shall 還可以表命令、警告、威脅；宣布法律、規(guī)定時(shí)，也要用shallYou shall leave the room at once, and he also shall.It has been announced that candidat

7、es shall remain in their seats until all the papers have been collected.四、 表示必要性1. must 常用來(lái)表示必要性，意為“必須”（1） must+do sth. （2） Dont have to do sth./ dont need to do sth./ neednt do sth（3） 表示過(guò)去沒(méi)必要做某事時(shí)，分為以下情況： neednt have done sth. Didnt have to do sth/ didnt need to do sth/ It was not necessary to do st

8、h.You neednt have worked that late last night. It was harmful to your health.-Did you work very late last night?-No, I didnt. I didnt need to work very late.Mustnt 意為“絕對(duì)不能，被禁止”You mustnt smoke here.2. should 也可以表示必要性，意為“（義務(wù)上）應(yīng)該”。Should 表示必要性時(shí)，在語(yǔ)氣上比must(必須)弱?！皊hould +動(dòng)詞原形”，表示現(xiàn)在或?qū)?lái)應(yīng)該做（的必要性）；“should+ h

9、ave+ 過(guò)去分詞”，表示過(guò)去本該做（的必要性）I should go and visit him this afternoon, but I wonder if I will be free.You should have come to the conference yesterday. What was the reason for your absence?五、 表示“寧愿做某事”時(shí)，可使用下面這些句式：Would rather do sth.Would rather do sth.than sth.Would do sth. Rather than do sth.Would rath

10、er sb. Did sth.Prefer to do sth.Prefer to do sth. Rather than do sthPrefer doing sth. To doing sth.六、“情態(tài)動(dòng)詞+have done”用法一覽表情態(tài)動(dòng)詞+have done用法例句Must have done想必/準(zhǔn)是/一定做了否定形式為：Can/ could have done本來(lái)能夠做過(guò)去可能會(huì)做Cannot/ could not have done過(guò)去不可能做了過(guò)去沒(méi)能夠做May/ might have done也許/或許已經(jīng)做.， 一般只用于肯定句或否定句在（再否定句中表示“可能不”，不

11、用于疑問(wèn)句中中。用might 則表示語(yǔ)氣更加不肯定。Should/ ought to have done本該做，而實(shí)際上未做Neednt have done本不必做而做了Had better have done當(dāng)時(shí)最好做了（其否定形式had better not have done表示相反的含義Would rather have done寧愿當(dāng)時(shí)做了（其否定式would rather not have done表達(dá)相反含義，兩者都表示“后悔”之意Would like/ love to have done sth.過(guò)去愿意做但未做成Shouldnt/ ought not to have done

12、本不該做而做了六、 情態(tài)動(dòng)詞的其他用法要點(diǎn)：1. cannot but +do sth.表示“不得不/只好做某事”I cannot but choose to go.2. may well 和may as well結(jié)構(gòu)（1）“may well + 動(dòng)詞原形”是一種常用結(jié)構(gòu)，意為“完全能，很可能”，相當(dāng)于“be very likely to +動(dòng)詞原形”He may well be proud of his son.Her appearance has changed so much that you may well not recognize her.(2) “may as well + 動(dòng)

13、詞原形” 意為“最好，滿可以，倒不如”You may as well do it at once.We may as well stay where we are.3.cannot (或can never 等)與enough 連用表示“再.也不為過(guò)”4.may 可以用于祈使句，表示祝愿May we never forget each other.May you return in safety.5.Why/ how + should結(jié)構(gòu)表示說(shuō)話人對(duì)某事不能理解，感到意外、驚訝等意思，意為“竟會(huì)”Why should you be so late today?How should I know?

14、6. must 表示“偏要、硬要“Must you make so much noise?If you must smoke, please go out.7. may 作“可以”講時(shí)，其否定式常用mustnt 表示 “禁止”；must 作必須講時(shí)，其否定式是neednt, 表示“不必”8. be able to 還有“設(shè)法做成”之意，相當(dāng)于manage to do 或succeed in doingMany people were able to escape from the fire.9.need 和dare 的用法Need 和dare 兩者既可用作情態(tài)動(dòng)詞也可用作行為動(dòng)詞。作行為動(dòng)詞時(shí)

15、，有人稱和數(shù)的變化，可用于肯定句、否定句或疑問(wèn)句中，構(gòu)成否定句或疑問(wèn)句時(shí)要用助動(dòng)詞do, does, did；作情態(tài)動(dòng)詞時(shí)，沒(méi)有人稱和數(shù)的變化（dare 的過(guò)去式為dared）,直接接動(dòng)詞原形，只用于否定句和疑問(wèn)句中，構(gòu)成否定句和疑問(wèn)句時(shí)不用助動(dòng)詞。 另外，dare作情態(tài)動(dòng)詞時(shí)，還可用于條件句中，過(guò)去式為dared；作行為動(dòng)詞時(shí)，dare常用于疑問(wèn)句或否定句，后面的to也可省略； Idare say 是習(xí)慣說(shuō)法，意為“我想，大概” 虛擬語(yǔ)氣一、 虛擬語(yǔ)氣在非真實(shí)條件句中的運(yùn)用從句主句例句與現(xiàn)在事實(shí)相反的假設(shè)If +主語(yǔ)+動(dòng)詞的過(guò)去式（be 動(dòng)詞用were）S + should/ would/c

16、ould/ might +動(dòng)詞原形與過(guò)去事實(shí)相反的假設(shè)If +主語(yǔ)+had + 過(guò)去分詞S + should/would/might/could + have + 過(guò)去分詞與將來(lái)事實(shí)相反的假設(shè)If +主語(yǔ)+動(dòng)詞的過(guò)去式If +主語(yǔ)+were to + 動(dòng)詞原形If + 主語(yǔ)+should + 動(dòng)詞原形S +should/would/could/might +動(dòng)詞原形使用虛擬條件句時(shí)要注意一下幾點(diǎn)：1. 當(dāng)條件狀語(yǔ)從句表示的行為和主句表示的行為所發(fā)生的時(shí)間不一致時(shí)，被稱為“錯(cuò)綜時(shí)間條件句”，動(dòng)詞的形式要根據(jù)它所表示的時(shí)間做出相應(yīng)的調(diào)整。If you had followed my advice

17、just now, you would be better now.If you had studied hard before, you would be a college student now.2. if 省略句在條件狀語(yǔ)從句中可省略，把were, had, should 提到句首，變?yōu)榈寡b句式If I were at school again, I would study harder.If you had come earlier, you would have caught the bus.If it should rain tomorrow, we would not go c

18、limbing.3. 含蓄條件句有時(shí)為了表達(dá)的需要，在虛擬語(yǔ)氣中并不總是出現(xiàn)if引導(dǎo)的條件狀語(yǔ)從句，而是通過(guò)其他手段來(lái)代替條件句。What would you do with one million dollars?Without your help, we couldnt have finished the work ahead of time.I was ill that day. Otherwise, I would have taken part in the sports meeting.He telephoned to inform me of your birthday, or

19、I would have known nothing about it.4. even if, even though也可用于虛擬語(yǔ)氣，其形式與if 從句在虛擬語(yǔ)氣中的形式相同。二、 虛擬語(yǔ)氣在名詞性從句中的運(yùn)用1. 用于賓語(yǔ)從句中（1） wish 后面的賓語(yǔ)從句一般用虛擬語(yǔ)氣，表示一種不可能實(shí)現(xiàn)的愿望。其謂語(yǔ)動(dòng)詞構(gòu)成形式為：過(guò)去式過(guò)去完成式Could/would +動(dòng)詞原形（2） 用于表示建議、愿望、命令等動(dòng)詞后的賓語(yǔ)從句中，常見(jiàn)的動(dòng)詞有：demand order require insist suggest recommend urge propose advise等。賓語(yǔ)從句中的虛擬語(yǔ)氣結(jié)構(gòu)為“should +動(dòng)詞原形”, should可以省略。He suggested that we should start off early the next day.They insisted that the boy s