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情态动词讲义情态动词讲义I.情态动词的语法特征情态动词本身虽有词义，但只表示说话人的看法，命令，准许等；不能单独作谓语，须与实义动词构成谓语1）情态动词除oughtto，haveto，usedto外，其它情态动词后面只能接不带to的不定式。2）情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。3）情态动词没有非谓语形式，即没有不定式to，分词-ing,-ed等形式。4）情态动词类别：can/cannot/cannot/can’t,may/maynot,must/mustn’t,shall/shallnot/shan’t,should/shouldn’t,oughtto/oughtn’tto,will/won’t,would/wouldn’t.need/needn’t,dare/daren’t,usedto/usedn’tto/didn’tuseto,haveto/don’thaveto,hadbetter/hadbetternot,wouldrather/wouldrathernotII.一些容易混淆的用法1.比较can和beableto1）can/could表示能力(bornability,learnedability),只用于现在式和过去式(could)。beableto可以用于多种时态。Peoplecanspeak.HecanspeakEnglishfluently.Acomputercan’tthinkforitself.Itmustbetoldwhattodo.Hesaidhecoulddotheworkbyhimself.cf:Theywillbeabletotellyouthenewssoon.他很快就能告诉你消息了。Hesaidhewouldbeabletogetapassportsoon.HehadbeenabletospeakalittleChinesebeforehecametoChina.2）只用beableto表示经过努力或在一定条件下设法成功地做了某事时，而非能力，只能用was/wereableto，不能用could。-----managedtodosth./succeededindoingsth.HewasabletofleeEuropebeforethewarbrokeout.=HemanagedtofleeEuropebeforethewarbrokeout.Aftertwoyearsofhardwork,hewasabletospeakEnglish.Althoughthedriverwasbadlyhurt,hewasabletoexplainwhathadhappened.Withthehelpofthefiremen,theywereabletoleavetheburninghouse.3)could不表示时态(1)提出委婉的请求，（注意在回答中不可用could）。---CouldIhavethetelevisionon?---Yes,youcan./No,youcan't.II.比较haveto和must1)两词都是'必须'的意思，haveto表示客观的需要，must表示说话人主观上的看法，既主观上的必要。Mybrotherwasveryill,soIhadtocallthedoctorinthemiddleofthenight.我弟弟病得很厉害，我只得半夜里把医生请来。(客观上需要做这件事)Iwanttotakemoreexercise,soImustwalktoschooleveryday.2）must表示必须，必要，一种义务，责任，职责,命令等语气e.g.Wemustobeytheschoolregulations.Youmustrespecttheold.Youmustcomehereearlytomorrow.IamafraidImustbeleaving.Wemuststayhome,mustn’twe?3）表示必然，必定,不可避免的结果Manmustdie.表示固执，一定要，坚持要e.g.Ourthree-year-oldboymustdotheoppositetowhatweordered.WhymustyouinterruptmenowandthenwhileIamspeaking.Mustyoushoutsoloudly?表示过去的不巧，偏偏e.g.JustwhenIwasbusy,theneighbormustcomeandchat.AsIwassittingdowntodinner,thetelephonemustring.4）haveto有人称、数、时态的变化，而must只有一种形式。e.g.Hehadtolookafterhissisteryesterday.Youwillhavetogotherealone.5）must问句的回答e.g.MustIwaituntiltheycome?---Yes,youmust.--No,youneedn’t./don’thaveto/don’tneedtoMustwehandinourEnglishexercisebookstoday?----_____________________./____________________6）在否定结构中：don'thaveto表示不必mustn't表示禁止，不允许，带有很强的语气e.g.Youdon'thavetotellhimaboutit.你不一定要把此事告诉他。Youmustn'ttellhimaboutit.你一定不要把这件事Carsmustn’tbeparkedhere.III.may表示给予许可1)Youmaysithere.MayIborrowyourbooks?MightIhaveyourtelephonenumber?2)can/could和may/might.can和may都可表示请求，或给与许可。Can语气一般，could/may比较礼貌，常用。对于can/could的回答,一般是can/can’t,不可用could，而对may的回答，则是may/maynot。----CouldIuseyourlegtop?----Yes,ofcourseyoucan./Sorry,Iamafraidyoucan’t.---MayIleavetheclassroom?---Yes,youmay./No,youmustn’t/youmaynot/youdon’thaveto.IV.情态动词can,could,may,might,must表示推测的用法1)can/could(1).Can/could用于疑问句表示猜测，可能,could一般不表示时态，只表达委婉语气.Whereishenow?Canhebereadinginthelibrary?Wherecantheyhavegone?(2).Can可表示理论上的可能性或偶尔的可能。Youcanwalkmilesandmilesthroughtheforestwithoutmeetinganyone.Heisverycleverboy,buthecanbedullsometimes.Evenexperiencedteacherscanmakemistakes.(3)can’t/couldn’t表示不可能;Couldn’t一般不表示时态，只表达委婉语气.但在过去时态的宾语从句只能用couldn’t.Ibelievehim.Hecan’tesuchanirresponsibleman.Shecan’thavegonetoschool.Wehavenoschooltoday.Ithoughtyoucouldn’thavemetheryesterday.2)may/might(1)may/might用于肯定句，表示没有把握的推测；might表示推测时，不表示时态,只是可能性比may小,但在过去时态的宾语从句只能用might.Petermaycomewithustonight,butheisn'tverysureyet.Hemightbeathome.Itmayhavedrizzledduringthenight.Philipmay(might)havebeenhurtseriouslyinthecaraccident.(2)maynot/mightn’t表示可能不，也许不。Hemaynotknowthetruth.3）mustmust用在肯定句中表示较有把握的推测，意为一定。Youhaveworkedhardallday.Youmustbetired.Hemustbeworkinginhisoffice.他一定在办公室工作呢。Ididn'thearthephone.Imusthavebeenasleep.4)这些表示推测的情态动词使用时的时态构成（1）情态动词+动词原形。表示对现在或将来的情况的推测，此时动词通常为系动词。Idon'tknowwheresheis,shemaybeinWuhan.（2）情态动词+动词现在进行时。表示对正在进行的情况进行推测。Atthismoment,ourteachermustbecorrectingourexampapers.这时，我们老师想必在批改试卷。（3）情态动词+动词完成时。表示对过去情况的推测。Theroadiswet.Itmusthaverainedlastnight.地是湿的，昨天晚上一定下雨了。(4)情态动词+动词的现在完成进行时。表示对过去正在发生事情或一个完成进行的动作的推测。Yourmothermusthavebeenlookingforyou.你妈妈一定一直在找你。5．表示推测的情态动词语气的强弱肯定语气---由强至弱mustmaymight否定语气---由强至弱can’tcouldn’tmaynotmightnot疑问语气can6)couldhavedone有两种含义。其一，表示本来有能力做但实际上没有；其二，表示差点就，幸亏没，带有幸而没发生的语气。IcouldhavewalkedtothestationifIhadknownitwassonear.Youwerestupidtothrowtheboxoutofthewindow.Itcouldhavehitsomeone.V.oughtto,should1)也可表示较大的可能性，（推测）Ifhestartedatsix,heoughtto/shouldbetherenow.Itisnearlyseveno’clocknow.Jackshouldbehereatanymoment.（应该，该）2）表示义务，责任,都为应该的意思，可用于各种人称。表示要求，命令时，语气由should（应该）、hadbetter最好）、must（必须）渐强。---Oughthetogo?---Yes.Ithinkheoughtto.Weoughtto/shouldlistencarefullyinclass.Youshouldbemorecarefulincrossingthestreet.Yououghttoleavenowifyoudon’twanttomissthetrain.3）should用于第一人称，表示说话人的谦逊，客气，委婉的语气Youaremistaken,Ishouldsay.依我看，你是搞错了Ishouldadviseyounottodothat.我倒是劝你别这样做。4）should用于引导的条件从句中，表示一件事听起来可能性很小，相当于“万一”Askhertoringmeupifyoushouldseeher.Ifyoushouldchangeyourmind,pleaseletusknow.Takeathickcoatincaseitshouldget/getscold.5)用于动词ask,advise,command,demand,insist,intend,recommend,r