1、定义情态动词(Modal verbs)本身有一定的词义，表示语气的单词。但是不能独立作谓语，只能和动词原形一起构成谓语。情态动词用在行为动词前，表示说话人对这一动作或状态的看法或主观设想。情态动词虽然数量不多，但用途广泛，主要有下列：can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would)。因为情态动词带有某种的情绪性，比如dare就很强硬，比较负面，而may就比较的和善，为了避免在谈话时把“讨论”变成“攻击”，宝贝们一定要学会善用情态动词哦!分类情态动词有四类：只做情态
2、动词：must,can(could),may(might),ought to可做情态动词又可做实义动词：need,dare可做情态动词又可做助动词：shall(should),will(would)具有情态动词特征：have(had) to,used to位置情态动词在句中放在谓语动词之前, 谓语动词前若有助动词,则在助动词之前,疑问句中，情态动词则在主语之前。I can see you. Come here.我能看见你，过来吧。He must have been away.他一定走了。What can I do for you?我能帮你吗?How dare you treat us like
3、 that!你怎能那样对待我们!特点情态动词无人称和数的变化, 情态动词后面跟的动词需用原形,否定式构成是在情态动词后面加 not。个别情态动词有现在式和过去式两种形式, 过去式用来表达更加客气, 委婉的语气, 时态性不强, 可用于过去，现在或将来。情态动词属非及物动词，故没有被动语态。情态动词没有非谓语形式，即没有不定式，分词，等形式。He could be here soon.他很快就来。We cant carry the heavy box.我们搬不动那箱子。Im sorry I cant help you.对不起，我帮不上你。基本助动词与情态助动词最主要的区别之一是，基本助动词本身没有
4、词义，而情态助动词则有自己的词义，能表示说话人对有关动作或状态的看法，或表示主观设想：What have you been doing since? (构成完成进行体，本身无词义)I am afraid I must be going. (一定要)You may have read some account of the matter. (或许已经)除此之外，情态助动词还有如下词法和句法特征：1) 除ought和used以外，其他情态动词后面只能接不带to的不定式。如果我们把ought to和used to看做是固定词组的话，那么，所有情态动词无一例外地只能接不带to的不定式：We used
5、to grow beautiful roses.I asked if he would come and repair my television set.2) 情态助动词在限定动词词组总是位居第一：They need not have been punished so severely.3) 情态助动词用于第三人称单数现在时的时候，没有词形变化，即其词尾无-s形式：She dare not say what she thinks.4) 情态动词没有非限定形式，即没有不定式和分词形式，也没有相应的动名词：Still, she neednt have run away.5) 情态助动词的“时”的
6、形式并不是时间区别的主要标志。在不少场合，情态助动词的现在时和过去时形式都可以表示现在、过去或将来时间：Would you mind very much if I ask you to do something?She told him he ought not to have done it.6) 情态助动词之间是相互排斥的，即在一个限定动词词组中只能出现一个情态助动词，但有时却可以与have和be基本助动词连用：You should have washed the wound.Well, you shouldnt be reading a novel.用法首先它是动词，而且不同于行为动词，
7、行为动词表示的是可以通过行为来表达的动作(如写，读，跑)，而情态动词只是表达的一种想法(如能，也许，敢)。用法是：情态动词+行为动词原形例句：I can read this sentence in English.我能用英语读这句话。情态动词是一种本身有一定的词义,表示说话人的情绪,态度或语气的动词,但不能单独作谓语,只能和其他动词原形构成谓语。We can be there on time tomorrow.我们明天能按时去那儿。May I have your name? 我能知道你的名字吗?Shall we begin now?我们现在就开始吗?You must obey the scho
8、ol rules.你必须遵守校规。功能助动词(auxiliary)主要有两类：基本助动词(primary auxiliary)和情态助动词(modal auxiliary)。基本助动词有三个：do, have和be;情态助动词有十三个：may, might; can, could; will, would; shall, should; must, need, dare, used to, ought to.上述两类助动词的共同特征是，在协助主动词构成限定动词词组时，具有作用词的功能：1) 构成否定式：He didnt go and neither did she.The meeting mi
9、ght not start until 5 oclock.2) 构成疑问式或附加疑问式：Must you leave right now?You have been learning French for 5 years, havent you?3) 构成修辞倒装：Nowhere can he obtain any information about his sister.Hardly had he arrived when she started complaining.4) 代替限定动词词组：A: Who can solve this crossword puzzle?B: Tom can
10、.A: Shall I write to him?B: Yes, do.用法要点can, could1) 表示能力(体力、知识、技能)。Can you lift this heavy box?(体力)Mary can speak three languages.(知识)Can you skate?(技能)此时可用be able to代替。Can只有一般现在时和一般过去式;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。如：He was able to
11、go to the party yesterday evening in spite of the heavy rain.2) 表示请求和允许。Can I go now?Yes, you can. / No, you cant.此时可与may互换。在疑问句中还可用could,might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中。Could I come to see you tomorrow? Yes, you can. ( No, Im afraid not. )3) 表示客观可能性(客观原因形成的能力)。Theyve changed the timetable, so we
12、can go by bus instead.This hall can hold 500 people at least.4) 表示推测(惊讶、怀疑、不相信的态度)，用于疑问句、否定句和感叹句中。Can this be true?This cant be done by him.How can this be true?特别说明：(1) could用来表示请求时，语气委婉，主要用于疑问句，不能用于肯定句，答语应用can(即：could不能用于现在时态的简略答语中)。Could I use your dictionary?Yes, you can.(否定回答可用：No, Im afraid no
13、t.)此时可与may互换。在疑问句中还可用could,might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中。Could I come to see you tomorrow?Yes, you can. ( No, Im afraid not. )(2) can和be able to辨析can(could)和be able to都可以表示能力，意思上没有区别。但can只有现在式和过去式，而be able to则有更多的形式。如：Ive always wanted to able to speak fluent English.Those bags look really heavy
14、, are you sure youll be able to carry them on your own?但是，表示在过去某时的某一场合经过一番努力，终于做成了某事，通常不用could，而用was/were able to来表示。could：有潜能，但并未做到，这时was/were able to相当于managed to do或succeed in doing。如：After the accident it was a long time before she was able to walk again.The fire was very big, but most people we
15、re able to escape from the building.I can sing many English songs.我会唱许多英文歌曲。We were able to return to our campsite before the heavy rain.我们在下大雨前设法会到了野营地。He was able to swim across the river and escaped being caught.他游到了河对岸，没有被抓住。在否定句中，can/could与be able t几乎没有什么差别，两者可以互换。例如：She wasnt able to/couldnt cook French dishes.她不会做法国菜。(3) 惯用形式“can not too”表示“无论怎么也不(过分)”。如：You cannot be too careful.你越小心越好。惯用形式“can not but+ 不定式(不带to)”表示“不得不，只好”。如：I can not but admire he
