1、情态动词情态动词一、情态动词的类型1.只作情态动词的有:must,can/could,may/might2.既可作情态动词也可作实义动词的有:need3.既可作情态动词也可作助动词的有:will/would,shall/should4.具有情态动词某些特征的有:have to,had better,used to,be able to二、情态动词的特征1.有一定的词义,但不能单独作谓语,必须和行为动词或系动词连用构成谓语。2.无人称和数的变化(have to例外,主语为第三人称单数时用has to)。如:We must stay here.我们必须待在这里。He has to walk hom
2、e.他不得不步行回家。3.后接动词原形。如:He can speak Japanese.他会说日语。4.具有助动词的作用,可用来构成否定句、疑问句及简明答语。如:Can we go home now,please?现在我们可以回家了吗?No,you cant.不,不可以。三、情态动词的用法(一)can和could的用法1.表示能力,意为“能,会”。如:Can you play basketball?你会打篮球吗?2.表示推测时,常用于否定句和疑问句中。如:It cant be Nicks.它不可能是尼克的。3.表示请求或允许,多用于口语中,意为“可以”,相当于may。如:You can/may
3、 go now.你现在可以走了。注意:以can开头的一般疑问句,其肯定回答和否定回答分别用can和cant。4.could是can的过去式,表示过去的能力;could也可在疑问句中表示委婉地提出请求。如:I could sing English songs when I was four years old.我四岁的时候就会唱英文歌曲。(二)may的用法1.表示推测,意为“可能;也许”,用于肯定句中。如:He may come tomorrow.他明天可能会来。2.表示请求、许可,意为“可以”。如:May I come in?我可以进来吗?注意:may表请求,用于主语为第一人称的一般疑问句时,
4、其否定回答用mustnt或cant,不用may not。3.表示祝愿。如:May you succeed!祝你成功!注意:can和may均可用来表示征求意见或请求许可,意为“可以”,一般可互换使用。(三)must的用法1.表示说话人的主观语气,意为“必须”。2.表示推测,意为“一定”,一般用于肯定句。在疑问句和否定句中表推测时一般应用can,否定句中也用may,但may not表示“可能不”,而cant 表示“不可能”。在否定句中,mustnt表示“禁止”,意为“千万不要”。以must开头的疑问句,肯定回答应用must;而否定回答则常用neednt,意为“不需要,不必”,相当于dont hav
5、e to,而不能用mustnt。must表示肯定的推测。结构结构作用作用must be+表语对现在状况的推测must be+现在分词对正在发生的事情的推测must have+过去分词对过去状况的推测拓展：拓展：must，should，may 和 might都可表示推测，可能性从大到小依次为：mustshouldmaymight。Theres someone knocking on the door.有人在敲门。It must be Jim.肯定是吉姆。Must I go home now?我现在必须回家吗?No,you neednt.不,不必。(四)对need词性的判断need后加to do说
6、明need为实义动词,用助动词提问或否定;若need后加动词原形,则need为情态动词,用need提问或否定。如:You neednt come to school so early.你不必这么早来学校。You dont need to leave now.你不必现在就走。(五)had better的用法had better do sth.表示“最好做某事”,否定式用:had better not do sth.。如:Youd better stay at home.你最好待在家里。(六)shall/should和will/would的用法1.shall用于第一人称,表示征求意见、询问。如:S
7、hall I open the window?要我开窗吗?Shall we say 6 oclock,then?那么,我们就定在6点钟好吗?2.should常用来表示义务、责任。如:We should obey the traffic rules.我们应该遵守交通规则。3.will 用于第二人称,表示询问、请求,也可以表达现在的意愿。如:Will you pass me that book?你能把那本书递给我吗?4.would 用来表示客气地请求别人做某事。如:Would you tell me the way to the station?你能告诉我去车站的路吗?四、几组情态动词的辨析1.c
8、an/could和be able to的区别 词语用法例句can/could只用于一般现在时(can)和一般过去时(could)Jim couldnt speak Chinese last year,but now he can.吉姆去年不会说汉语,但现在他会了。be able to可用于多种时态We will be able to come back next week.我们下周能回来。2.can 和may表可能的区别(1)在肯定句中,用may表示可能。如:You had better ask that policeman.He may know.你最好问那个警察,他可能知道。(2)在否定句
9、中,cannot/cant和may not的区别。词语用法例句cannot/cant语气肯定,意为“不可能”Mr Li cant be in the room.He has gone to Beijing.李先生不可能在房间里,他去北京了。may not语气不肯定,意为“可能不”Is John coming by train?约翰是坐火车来吗?He may not.He likes driving his car.可能不是。他喜欢开他的小汽车。3.must和have/has to的区别4.cant和mustnt的区别词语用法例句must表示主观意愿,意为“必须”We must study ha
10、rd at school.在学校我们必须努力学习。have/has to用于强调客观需要,意为“必须,不得不”Well have to ask Zhang Hong.我们得去问张红。词语用法例句cant表示否定推测,意为“不可能”He cant be Jim.他不可能是吉姆。mustnt表示“禁止、不允许”,不能用来表推测You mustnt play soccer in the street.你千万别在街上踢足球。1._ you pass me a pen?Id like to write down the phone number.Sure.Here it is.A.Can B.Need
11、C.Might 2.May I go to the cinema,Mum?Certainly,but you _ be back by 11 oclock.A.can B.may C.must 3.You _worry about me.Its nothing serious.A.cant B.mustnt C.neednt ACC4.I called you yesterday.A woman answered,but I didnt recognize her voice.Oh,it _ my aunt Jean.A.must be B.must have been C.might be
12、5.Excuse me.Is this the right way to the Summer Palace?Sorry,Im not sure.But it _ be.A.might B.mustnt C.must6.Can you go skating with us this afternoon？Sorry,I cant.I _ take care of my little sister at home.A.can B.may C.have toAAC 7._I have your English name，please？Yes，Helen.H-E-L-E-N.A.Must B.May
13、C.Will 8.Must we clean the room right now？No,you _.You _clean it after lunch.A.neednt；may B.neednt;must C.mustnt;can 9.You must come back every month.Yes，I _.A.will B.must C.should BAA10.Children _ play with fire.A.mustnt B.cant C.shouldnt 11.-Is Mr.Smith swimming in the pool,Harry?-It _ be him.I sa
14、w him go to the library just now.A.may not B.cant C.neednt12.Can I borrow your dictionary?Yes,you _.A.can B.must C.shouldABA13.Finally,they came back.They _be hungry after such a long walk.Acant Bmust Cneednt14.Mum,Im going climbing.Must I clean the room now?No,you_.You can do it this evening.A.cant B.mustnt C.needntBC15.The passengers _ show their ID cards before getting on the plane.A.mightB.mustC.could16.-Mum,_ I visit the Science Museum tomorrow?-Im afraid you cant.It is closed on Monday.A.must B.may C.shouldBB
