助动词Auxiliary英语动词,按其在构成动词词组所起的作用,分为主动词（Main Verb）和和助动词（Auxiliary）两大类。

助动词又分为基本助动词、情态助动词、和半助动词。

情态助动词的语法特征是，没有非限定形式，没有词形屈折变化。

I、情态动词意义表示法A．表示“能力”和“可能”1．表示“能力”（Ability），can，could，be able to。

a.既能表示现在的“能力”,也能表示将来的“能力”。

I can drive the car.Y eah，I can do it at the moment.Tom can solve on time.I can’t do it, but I can do that.Look, you can make out this problem now.b.用can表示现在的“能力”,既可以表示做某桩具体事情的“能力”,也可以泛指一般的能力Diligence can make your outlook brighter.I don’t think Tom can pass the exam.Can I do you a favor?Having this class can improve your oral English.Never can he play football any more.c.表示过去的能力,可用could和was/were able to, 但在肯定句中,could所表示的能力仅是泛指过去的一般能力Tom was able to work under high pressure and time limitation.Will we be able to select more than 12 units at the same time?Cindy was able to speak when she was 1 year old.You could hear the carol from the chapel before this factory has been build.A good translator is able to communicate in professional language and have goodnegotiation skills.d.表示过去某桩具体事情的能力,通常不用could,而用was/were able toTerry was able to ride bike before he had the surgery.Zoe’s factory was able to pay for the service before the economic crisis.Sam was able to pass the exam without any training.Richard was able to finish the project with his wife’s help.We were able to cross the river without a bridge there.2. 表示“可能”,可用may, might, can, could. may/might表示”可能”,往往可以交替使用,并无时间上的差异,只是用might在口气上比用may更加不肯定,从而比较委婉.a. may/might既可以表示现在的可能,也可以表示将来的可能That may/might be the reason why you don’t achieve your objective.He may/might get the present at the performance now.That may/might be the result of this case.Crime may/might be a threatened of the society nowadays.This boss may/might give you more than that one.b.在疑问句中表示可能,须用can而不用mayWhat can I do for you?Can you help me?Can I help you?Can you tell me how to get there?Where can she live when she got there?c.用can表示可能,较多的用于否定句和疑问句,而could则不受此限You could call me if you need my help.Can the monkey climb on the tree in 3 seconds?It could be a suitable way for you to grapple with this matter.The man could be a crime of this case.Can you have missed the train?d.在肯定句中,用can表示可能与用may表示可能往往产生含义上的微妙差别:用can表示可能往往指逻辑上的可能性;而用may表示可能则指事实上的可能性The train may be delayed. (It is possible that the train was delayed.)The train can be delayed. (It is possible for the train to be delayed.)You can miss the bus today. (It is possible for you to miss the bus.)You may miss the bus today. (It is possible that you miss the bus.)3.表示过去的可能,可用may/might+不定式完成体或不定式完成进行体,在这里用may/might,也只有口气上婉转程度的差异,而没有时间上的差别.You may/might have got a prefect life.She may/might have a wonderful job at that moment.I may/might have been student of senior high school already.He may/might have got a good mark in the final exam last semester.He may/might have brought that car already.B、表示“许可”和“不许”1、请求对方许可用can, could, may, might.a. may/might与can/could相比,前者比较正式;may/can与might/could相比,后者较为婉转,更有礼貌.在口语中特别常用can表示许可Can/Could; May/Might I smoke in here.Yes, you can.Can I take the seat?Can I have the bill?Could you please come here?b. 表示给予许可通常用can/may,而不用could/might.Could I use your phone? Yes, you can.Might I take you one minute? Yes, you may.Could I take the seat? Yes, you canCould I borrow your pen? Yes, you can.c. 用may/can与might/could都不存在时间的差异,但在上下文中,便存在这种差异.Anyone may/can enroll for this course.All students may/can go now.In those days anyone might/could enroll for this course.Last week, all students might/could go now.2、表示不许可用may not或者cannota. may not也可表示一般的不许可,即表示根据一般规定,而不是说话人不许可.He may not keep more than two books more than a week from library.He may not bring the food to the shop.He may not bring his pet to the bus.He may not get some food from the library.C、表示“义务”和“必然”1. 所谓表示义务,即表示必须,应该做某事.表示这些意义,可用should, ought to, must.用这三个情态助动词表示义务,其语气强弱略有差异.a) 用should/ought to表示应该,带有表示劝说或敦促的含义We should learn from the model workersYou should do what your teachers tell youHe should do something to help herWe should clean up the classroom after classWe should hand on our homework in this weekb) Should与ought to同义,都能表示应该,往往可以交替使用.用should口气比较肯定一些,说话人的主观信心要强烈一些,而用ought to则在语气上不是那么坚定.You should/ought to drink lessYou should/ought to tell the policeHe shouldn’t/oughtn’t to stay up so lateI should go nowI should go to bedc) 用must表示敦促或命令,在口气上比should更加强烈,这意味着说话人是权威的一方,对人对己都适用.We must do it againYou must hand on your homeworkYou must be back by 10 o’clockI really must stop smokingd) 表示必须,must与have to意义接近,但在用法上略有区别:用must表示必须,侧重于说话人的主观一直,用have to表示必须则侧重于客观的需要.He must say it in English. He has to say it in EnglishHe must move the furniture himself. He has to move the furniture himself.He must go to school on foot. He has to go to school on foot.e) 在特定语境中,用will也可以表示义务.常用于第二人称主语,这实际上是一种强化的祈使句,比带有第二人称主语的祈使句口气更为强化You will wait outside the gateYou will report to me afternoonYou will tell me the truthYou will do it yourself2. 所谓表示必然就是根据说话人的判断和推测认为必然会有某种情况.表示这种意义,可用should, ought to和must,其中以用must口气最为肯定.a) 用should表示必然,指说话人根据一定情况做出推测或者推断She should be here in a minuteThe book should appeal to all lovers of poetryThat should not be difficult problem of MaryHe should leave nowb) 用ought to表示必然也是根据一定情况做出推测或推断.用ought to表示推断或推测与must同义,但语气较弱,从而也比较委婉.These young trees ought to provide shade in ten yearsHe ought to be able to help youHe ought to give you a handThese ought to be kept safec) 用must表示必然,也是推断或推断,其口气最为肯定,一般用于可定陈述句.All men must dieCareless reading must give poor resultsIt must be very late because the streets are quite desertedYour father must be expecting you homeHe must be excited if you tell him theseD、表示“预见”和“推测”1. 表示预见,即表示单纯将来,可用will/shall+不定式a) will可用于一切人称表示将来I will be a different person when I live in EnglandWe will have a great time if we go to the partyYou will be hearing from meWhat will you do when the war is over?She’ll probably last longer than you willb) 非正式用语中,will更是常用于第一人称主语表示将来,尤其常用will/shall的缩略形式’ll, 从而进一步模糊了will/shall的界限I’ll book a table at the shopI’ll come in after church and give you a handWe’ll be going on later for bridgeWe’ll go to the party if we are invited2. 表示推测,除用should, ought to和must外,还可用will/would用will/would表示推测可有三种情况a) 对特定事态的推测That won’t be himShe will be all right nowBy now he will be eating dinnerThey will have arrived by nowb) 对某些习惯性事态的推测,用will指现在习惯,用would指过去习惯A lion will attack a man only when hungryHe will work all day without a restHe will stay at home all dayEvery day she will sit there for hour doing nothingc) 对某些不受时限的客观过程的推测,只用will,表示现在时间,可与一般现在时的类似用法交替使用Oil will float on waterPigs will eat anythingLeaves will turn yellow in autumnE、表示“意愿”、“意图”和“决心”1. 表示意愿,即愿意做某事,可用will, would, shall.a) 用will表示意愿,可用于一切人称的主语I will lend you the money if you need itWho will go with meMy sister will help youYou can help me if you willb) 表示过去的意愿或过去不愿意做某事,可用would和would notI asked him if he would help meI wouldn’t read any bookHe would never do anything like thatc) 用shall表示意愿一般适用第二三人称主语,在疑问句中是征询听话人的意愿You shall stay with us as long as you likeHe shall be praised if he works for the peopleShall you take a holiday this summer?Shall my daughter do the shopping for you?2. 表示意图,即打算做某事,也可用will, would, shalla) 用will表示意图,可用于一切人称主语I will write to youWhy will you go there?I will get some drinkWhat will you want?b) 表示过去的意图或用在间接引语中可用wouldHe would see her the next dayHe wouldn’t have any cold drinksHe wouldn’t write to herHe would talk to herc) 用shall表示意图用于疑问句中式征询听话人的意见或意图Shall I walk with you?Shall I borrow your pen?Shall I take the seat?Shall I ask you a question?3. 表示决心,即坚持要做某事, 也可用will, would, shalla.用will表示决心或坚持决心或坚持,可用于一切人称的主语I will take the jobI won’t go back on my wordsHe will go out without moneyb.表示过去的决心,即过去坚持做某事,便可用wouldShe would married himHe would climb the mountain regardless of dangerThe annoying thing was that she would make a muddle of almost anythingc. Shall表示决心主要用于第二三人称主语, 表示说话人的强烈意志和决心You shall obey my ordersHe shall leave the country at onceThey shall do what I told them doF、其他情态意义1、shoulda、should可以在某些语境中表示惋惜、忧虑、欢欣、惊讶等感情色彩It’s a pity that he should leave so soonThey were sorely distressed that their motherland should be in such great dangerThey were amazed that she should have done so much in so short a timeIt’s unbelievable that he should be working so hardIt’s marvelous that somebody should have imaginations like thatb、可用在某些语境中并不表示具体的情态意义I insisted that he should go with meIt is imperative that we should have a strong air forceThe order that all civilians should be evacuated was soon carried out2、woulda、would可用于委婉的陈述I don’t think he would be so carelessIt would be a shame to stop our work halfwayIt would be done by meb、可用于客气的请求Would you like to stay here for the night?What would you advise me to do?Would you please come here?Would you come with me?c、用于委婉的建议Wouldn’t it be better for us to start off a little earlier?It wouldn’t be a bad idea for us to hold two separate meetings for the two problemIt would be done in this way3、darea、作为情态助动词表示胆敢，dare通常只用于否定陈述句和疑问句I dare not go thereHe dare not jump from the top of the wallHow dare he say such rude things about me?b、dare还可用作助动词。