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1、情态动词情态动词（modelverb）用来表示能力、允许、可能、必须、劝告、意愿等概念或态度。主要的情态动词有can（could），may（might），shall（should），will（would），must，oughtto，need，dare等。情态动词没有人称和数的变化，其后常跟不带to的不定式。1.情态动词的一般用法：l(1)表示能力:can,could,beabletolHe is over 80 but still can read withoutglasses.lShecouldntcomeyesterday.lHecantcometomorrow.llcan/could与b
2、eableto用法比较l1）beableto除有一般现在时、一般过去时、一般将来时外，还可有现在完成时、不定式、动词-ing形式等。lThisistheinformationIvebeenabletogetsofar.lTobeabletorideabike,shepracticedalot.lJustbeingabletodriveahorse,acartisntmuchhelptous.l2)could表示过去总的、经常性的能力；was/wereableto表示过去具体情况下具有的能力，并且做了某动作。lHecouldspeakFrench,sohewasabletoshowtheFren
3、chladytheway.l3)表示将来的能力常用willbeableto.lWhenwillyoubeabletotakeustotown?(2)(2)表示许可：表示许可：can/could,may/might;cant,maycan/could,may/might;cant,maynot,mustnt,mustnotnot,mustnt,mustnotl1)征询“许可”或给予“许可”可用can/could或may/might表示。May用于正式场合，can用于非正式场合，could用于客气的询问，might极少用。lYoucangoatfouroclock.lCouldIborrowyou
4、rpen?lStudentsmaytake3bookseach.lMightIaskwhetheryouareusingthetypewriter?l2)表示“不允许”用cant,maynot,mustnt；mustnot语气重。lYoucantleavethetableunlessyoufinishyourmeal.lPutthatcigaretteout.Youmustnotsmokenearapetrolpump!l3)表示过去“许可”不用could，might，要用其他表达方式。lWehadbeen/weregivenpermissiontospeaktothepatient.l但在间
5、接引语中表达过去“许可”，可用could，might。lThenursesaidthatwecould/mightspeaktothepatientforjustafewminutes.(3)(3)表示可能性：表示可能性：may/might,can/could,must;may/might,can/could,must;cantcantl1）may,might用来推测现在“可能”；may比might表示的可能性大些。lWhyisntJohninclass?Hemay/mightbesick.lmaybe是副词，不是情态动词。Maybeheissick.l2)在日常口语中常用can/could表
6、示“可能”。lYoucan/couldwalkformilesinthecountrywithoutmeetinganyone.lCanthenewsbetrue?No,itcantbetrue.l3)must表示可能性最大，“必定”；否定形式用cant表示“肯定不”、“必定不会”。lYoumustbehungryafteralongwalk.lThe phone is ringing,but there is no answer.She cant be athome.（4）表示必须和需要：must,haveto,needl1）must表示说话人认为“必须”；否定回答时用neednt“不必”。
7、lYoumustbehereatnineoclock.lMustyougosoon?No,Ineedntgoyet.l2)haveto表示他人或客观情况要求“必须”。lIhavetobebackatschoolbyeight.Ihavealotofworktodotonight.lWedonthavetowearuniformsinschool.ll口语中常用havegotto表示“必须”。lIhavegottoleavenow.Ihaveameetingintenminutes.l3)need表示动作者“需要”、“有必要”，用于否定句或疑问句；肯定回答用must，否定回答用neednt。lN
8、eed he go now?Yes,he must.No heneednt.llneed常用作实义动词。lYouneedtolearnthevalueoftime.lYoudidntneedtotellhimthenews.lDoessheneedtogo?l（5 5）表示责任和劝告）表示责任和劝告:should,oughtto,must,hadbettershould,oughtto,must,hadbetter l1)用should和oughtto表示责任和劝告，后者的语气重些lYoushould/oughttodoasyouaretold.lSuchthingsshouldnt/ough
9、tnottobeallowed.l2)有时也用must表示责任和劝告。lYoumustseethemovie.Itswonderful.l3)口语中也常用hadbetter表示劝告，意为“最好做/不做某事”。lYouhadbettertakecareofyourself.lYoudbetternotmakeamistakenexttime.lHadntyoubetterseewhoisatthedoor?（6 6）表示建议：）表示建议：shallshall，may/mightaswell,may/mightaswell,may/mightjustaswellmay/mightjustaswel
10、l l1)“shallI/we”表示征求对方对建议的看法。lShallwecarrytheboxesintothehouse?lLetsgo,shallwe?l2)may/mightaswell,may/mightjustaswell表示推荐更佳方案，建议另一种做法，意为“倒不如”，“不也一样吗？”。lWemayaswellstayheretonight.lYoumightjustaswelltellthetruth.(7)表示许诺：shalllshall用于第二、三人称，表示说话人的许诺。lYoushallhaveyourmoneybacknextweek.lIfhepassestheexa
11、m,heshallhaveaholiday.(8)表示意愿：shall,will/wouldl1)you/he/theyshall表示说话人的强烈意愿，甚至威胁。lYoushallpayforthis.lTheyshalldowhatItellthemtodo.ll在法律条文、规章制度中，shall表示“必须”。lEachcompetitorshallwearanumber.l2)will/would表示动作者愿意。lIwilllendyouthebookifyouneedit.lIwontdoitagain.lIhavebeentryingtoopenthedoor,butthekeywon
12、tturn.ll“willyou/wouldyou”在下列句中表示客气的建议、询问。lWillyoupleasehaveadrink?lWouldyoupleasepassmethesalt?lWouldyoulikeacupoftea?lWouldyoumindifIopenedthewindow?lWouldyoumindopeningthewindow?Wouldyoumindmyopeningthewindow?llwould还表示过去的习惯。等于usedtolOnSundayshewouldgetupearlyandgofishing.l(9)表示勇敢：dare ldare表示“敢于
13、”，用于否定句、疑问句或条件句。lHedarenottry.lHowdareyouopentheletter?lIfyoudaresayaword,Illstrikeyoudown.lldare还常用作实义动词。lHedaretosurfinheavywaters.lldaresay或daresay，表示probably,Isuppose.lIdaresayhewillcomehomelate.2.情态动词的特殊用法l（1）情态动词+不定式完成时l1）can/could,may/might,must+have+动词的过去分词l用于肯定句：表示对过去事件的主观判断，推测过去某动作“可能”、“也许
14、”、“一定”已发生。lTom could have taken the dictionary.I saw him using it lastSunday.lIcantfindmysunglasses.Imay/mighthaveleftthemattherestaurantyesterday.lYou screamed in your sleep last night.You must have had aterribledream.l用于否定句：表示推测过去某动作“可能”、“也许”、“一定”没有发生。lShecouldnthavefinishedherworksosoon.lShemayno
15、thaveseenyou.lDadmustnthavewashedthedisheslastnight.l2)should/oughtto+have+动词的过去分词。l用于肯定句：评论过去“应该做”而实际并未做的动作，意为“本应该”。lIdidntaskher.Itsapity.Youshouldhaveaskedher.Yououghttohaveaskedeveryone.l用于否定句：评论过去“不应该做”而实际做了的动作，意为“本不应该”。lIonlytoldMike.Youshouldnthavetoldanyone.Yououghtnottohavetoldanyone.l3)nee
16、dnt+have+动词的过去分词l对过去已经发生的动作进行评论，认为“无须发生”，“不必做”。lIneednthaveputonmybestsuittogototheparty;mostoftheguestswerewearingjeans.lWe went to the meeting,but it had beencancelled.Oh,soyouneednthavegone.(2)情态动词+不定式进行时 l表示推测或评论某动作现在是否正在进行。lShemaybewashingherclothes.lHecantbeworkingnow.lHemustbestudyinginthelibrary.lTheyshouldntbewatchingTVnow.Theyshouldbedoinghomework.(3)情态动词+不定式完成进行时 情态动词+havebeen+动词的现在分词，表示推测或评论过去某动作是否正在进行或一直在进行。Hemayhavebeenbuyingstampsinthepostofficewhenyousawhim.Shemusthavebeenworkingthen.Sheshouldhavebeenattendingameetingyesterdaymorning.Theyshouldnthavebeenchattingwhileworking.