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1、情态动词的概述,情态动词的定义：表示说话人对有关动作或状态的看法，或表示主观设想，如表示可能、怀疑、允诺、愿望、义务、必要、猜测等。不能单独做谓语，必须和行为动词的联系动词一起构成谓语。掌握情态动词的语法特征：1）只表示期待或估计某事的发生。2）情态动词没有人称，数的变化。情态动词后必须跟动词原形。掌握常用情态动词：can,could,may,might,must,need,shall,will,should,would等的用法。,一、can,could,1)表示能力（体力、知识、技能）“能，会”。Can you lift this heavy box?（体力）Mary can speak t
2、hree languages.（知识）Can you skate?（技能）在表示能力时can,could可用be able to代替。但是Can只有一般现在时和一般过去式,在过去式中用could；而be able to则有更多的时态。Ill not be able to come this afternoon.当表示“经过努力才得以做成功某事”时应用be able to，不能用Can。He was able to go to the party yesterday evening in spite of the heavy rain.,2)表示请求和允许。,-Can/Could come to
3、 my party?-Sure,Id love to.用在疑问句里表示请求许可时,can和could都可用于一般现在时,但could比can语气更加委婉。-Could you please take out the trash?-Yes,sure./Yes,Id love to./All right./Ok./Certainly./No problem.(肯定回答）-Sorry,I have to./I am going to./Im afraid./oh,please dont.（否定回答）,3)表推测可能性。,肯定句中：can表示理论上的可能性；may表示事实上的可能性，如：In Tibe
4、t,sometimes it can be really cold.Tom may go camping with us tomorrow,but he is not sure.备注：否定句和疑问句中，只能用can表猜测可能性。-Someone is knocking at the door,and who can it be?-It cant be Tom because he has gone to Beijing.（have gone to到某地去,说话人不在现场。have been to曾去过某地，现在已不在那里了，后面可接次数。have been in 在某地呆了多少时间”，常与时间
5、段状语连用。）,4）表示能力，意思是“能”“会”，其否定形式为cant/cannotI cant swim very well.5)在口语中，can可以代替may，表示“应许”You can keep this book for two weeks.,二.should/shall,表示“应该”，常用来表示劝告、建议；认为和ought to 同义。认为“某人应该做某事”或“有义务责任做某事”。You should lie down and rest.We should obey traffic laws.2)用于第一人称，表示征求对方意见。What shall we do this mornin
6、g.3)用于第一三人称疑问句中，表示说话人征求对方的意见或向对方请示。Shall we begin our lesson?,4）用于第二、三人称，表示说话人给对方的命令，警告，威胁。He shall be punished.5)它可以和 ought to，be supposed to 互换使用。6)Should(ought to)表示推测时，是指有一定根据的推测，意为“可能、该”-When can I come for the photos?I need them tomorrow,-They _ be ready by 12:00,3)Should(ought to)表示推测时，是指有一定根
7、据的推测，意为“可能、该”,-When can I come for the photos?I need them tomorrow,-They _ be ready by 12:00,三.will 和would,1)表示意志或意愿：决心，愿意，We will do our best to save the child.我们会尽力抢救这个孩子。I told her to stop crying,but she just wouldnt listen.我叫她别哭,可她就是不愿听。2)表示请求、建议或征求对方意见时，用Would you?比用Will you?更婉转。Will/Would you
8、please keep the door open?请让门开着好吗？,相关情态动词：would like表示愿意I would like to have a word with you.我想同你说句话。would ratherthan宁愿也不愿I would rather fail than cheat in the test.我宁愿考不及格，也不愿意考试作弊。had better 意为“最好”，后接不带to的不定式,即had better do sth。We had better go now.(we had better=wed better),四.must,1)表示“必须”、“必要”,是
9、说话人的主观看法，通常用于现在时。其否定形式为neednt.“不必”。-Must we hand in our exercise books today?-Yes,you must.-No,you dont have to/you neednt.（否定回答只能用neednt,dont have to“不必”,不能用mustnt禁止，不准）2)表示“推测”，意思是“一定”“准是”（只用于肯定的陈述句）Your mother must be waiting for you now.,3)表示义务意思是应该，其否定形式为mustntYou mustnt speak like that.4)must和
10、have to的区别：都表示“必须”但是must 强调客主观上的必须，have to强调客观上的必须，“不得不”，并且可以用其他的形式来表达。Its late,I must go now.I have to wash all my clothes.,五.Might and may,表示请求和允许。might比 may语气更委婉，而不是过去式。其否定形式为may not或mustnt表示“不准“不应该”，否定回答时可用cant 或mustnt，表示“不可以，禁止”。-May/Might I take this book out of the room?-Yes,you can.(No,you c
11、ant/mustnt.)用May I.？征徇对方许可时比较正式和客气，而用Can I.？在口语中更常见。,2）用于祈使句，表示祝愿。May you succeed!3)表示推测,可能性（不用于疑问句）。might不是过去式，它所表示的可能性比may小。He may/might be very busy now.Your mother may/might not know the truth.,六.need,1need表示“需要”多用于否定句，其否定形式为neednt,意思是“不必”其反义词一般为must“必须”。-Must I finish homework now?-Yes,you must
12、.-No,you neednt.2由need引出的一般疑问句，肯定回答常用must或haveto;否定答语常用neednt.NeedIanswerthequestion?我需要回答那个问题吗？Yes,youmust/haveto.是的，你必须回答。-No,youneednt./dont have to不，不必了。,由must引出的一般疑问句，肯定回答用must,否定答语用neednt或donthaveto。,MustIdotheworknow?我必须现在干这个活吗？Yes,youmust/haveto.-No,youneednt/donthaveto.Need 做行为动词Need sthNee
13、d to do sthNeed doing=need to be done表被动否定：dont need,七.dare 敢,通常用于疑问句、否定句或条件句中Dare you ask him?你敢问他吗？I dont know whether he dare try.我不知道他敢不敢试。注意:有过去式dared。如：1.No one dared speak of it.没有人敢提及此2.How dare you/he/she/they?表示说话人对某人的行为表示愤慨。如：How dare you ask me such a question?你怎敢问我这样的问题?3.I dare say表示“我
14、相信，我认为，可能”。如I dare say you are right.我认为你是对的,作行为动词：可用于各种句子中；在疑问句或否定句中，to经常被省略。,Did anyone dare(to)admit it?有人敢于承认吗?He did not dare(to)leave his car there.他不敢把车停放在那里.If he dares to show up at her house Ill be surprised.如果他敢出现在她的房子里，我会感到吃惊。,二、表推测的用法,1.must have done过去肯定做了某事 Since the road is wet,it mu
15、st have rained last night.不存在 mustnt have done 的形式。其否定或疑问形式须用 can(could)来表示.例如：He cant have missed the way.I drew him a map.“The dictionary has disappeared.Who could have taken it?”,注意点一：,表推测可能性：must,can,may,might,cant,couldnt-I heard they went skiing in the mountains last winter.-it _ true because
16、there was little snow where.,即讲即练,1._ I go out to play now，Mum?No，you_ AMay，shouldnt BCan，neednt CMust，cant DMaymustnt 2.Help me with this case_ you?Adont Bwill Cdo Dshall 3.They started early that morning in order that they_ there before noon Amight get Bmay get Cwould get Dgot,二.may/might have don
17、e,I cant find my keys.I may/might have left them at the school yesterday.我找不到我的钥匙了。我可能昨天把他们落在学校了。John may/might not have passed the exam;he looks very sad.约翰可能没有通过考试。他看起来很忧伤。,三.can/could have done 表推测一般用在否定句和疑问句中，表示不相信或怀疑的态度。,Can/Could he have passed the exam?他可能通过了考试吗？I think that he couldnt/cant h
18、ave gone abroad.I saw him just now.我认为他不可能出国了。我刚才还看见他了。,1.If you _ do as I tell you，you_ go to the party Acan，shant Bwill,wontCwont，shall D wont,shant 2.A teacher do every exercise，but a pupil_Aneednt，must Bmay not，mustCneednt,neednt Dcant,must3.Dont believe himHis story _ be true Amustnt Bneednt Cshouldnt Dmay not,4.-She must have gone back to the valley-No,she _.The entrance to it was nowhere to be found Amustnt Bneednt Ccouldnt Dhadnt 5.You need not do it at once,_?Aneednt you Bmustnt you Cdont you Dneed you 6.He must be in the classroom_ he?Amustnt Bcant Cisnt DCan,Thank You!,
