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1、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/shallno
2、t/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,learnedab
3、ility),只用于现在式和过去式(could)。beableto可以用于多种时态。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.Aftertwoyearsofha
4、rdwork,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
5、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.Wemustobeyt
6、heschoolregulations.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.WhymustyouinterruptmenowandthenwhileIamspea
7、king.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.MustIwaituntilth
8、eycome?---Yes,youmust.--No,youneedn’t./don’thaveto/don’tneedtoMustwehandinourEnglishexercisebookstoday?----_____________________./____________________6)在否定结构中:don'thaveto 表示"不必"