情态动词
定义:
  情态动词是一种本身有一定的词义,但要与动词原形一起使用,给谓语动词增添情态彩,表示说话人对有关行为或事物的态度和看法,认为其可能、应该或必要等。
  情态动词后面加动词原形。
分类:
  情态动词有四类:
  只做情态动词: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 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 can't carry the heavy box.
  我们搬不动那箱子。
  I'm sorry I can't 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)
see you tonight  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 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 needn't have run away.
  5) 情态助动词的“时”的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 shouldn't be reading a novel.
用法
  首先它是动词,而且不同于行为动词,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 school rules.你必须遵守校规。
  情态动词数量不多,但用途广泛,主要有下列:
  can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would),have (to) ,had better.
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 didn't go and neither did she.
  The meeting might not start until 5 o'clock.
  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, haven't 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.
  A: Shall I write to him?
B: Yes, do.
                      情态动词的用法要点
一.can和could
情态动词
用法
例句
can/could
表示能力(体力、知识、技能)
(表示过去有能力用could)
1.I dont think Mike can type.
2.I can speak fluent English now , but I couldnt last year.
3.Can you lift this heavy box?(体力)
4.Mary can speak three languages.(知识)
5.Can you skate?(技能)
6.Two eyes can see more than one. 两只眼比一只眼看得清。
7.Could the girl read before she went to school? 这女孩上学前能识字吗?
在肯定句中,表示客观可能性,(客观原因形成的能力)。并不涉及具体某事会发生,常用来说明人或事物的特征。要表达具体某事实际发生的可能性时,不用can,需用could,may,might。
1.As a human being, anyone can make a mistake.
2.Im confident that a solution can be found.
3.He can be very forgetful sometimes.
4.I may stay at home this weekend.(实际可能性)
5.Peter might come to join us.(实际可能性)
6.It will be sunny in the daytime ,but it could rain tonight.(实际可能性)
7.7.They’ve changed the timetable, so we can go by bus instead.
8.8.This hall can hold 500 people at least.
9.The temperature can fall to –60, that is 60 below freezing.
气温可降至—60,也就是零下60
10.11..He can´t (couldn´t) have enough money for a new car. 他不可能有足够的钱买新车。
11.12 You mustn´t smoke while you´re walking around in the wood. You could start a fire. (实际可能性)
12.在林子里走时勿吸烟,那样可能会引起火灾。
表示请求和允许。表示请求,口语中常用could代替can,使语气更委婉。
用can和 may来回答,不能用could或might。
1.Can we turn the air conditioner on?
2.Any police officer can insist on seeing a drivers license.
3.In soccer, you cant touch the ball with your hands.
4.Could you have her call me back when she gets home, please?
5.I wonder if I could just ask you to sign this.
6. Could I borrow your dictionary?
---Yes, of course, you can.
No, I'm afraid not/No,you cannt/No,you may not.
表示对现在的动作或状态进行主观的猜测,主要用在否定句和疑问句中。
1.It cant be easy caring for a man and a child who are not your own.
2.Can the man over there be our head master?
3.If Tom didn't leave here until five o'clock, he can't be home yet. 如果汤姆五点才离开这儿,他此时一定还未到家。
表示惊异、怀疑、不相信等态度,主要用在否定句、疑问句和感叹句中。
2.Can this be an excuse for not giving them help?
3.This cant be true.
4.How can you be so crazy.
5.4.Can this be true?
6.5.How can you be so careless!
7.6.This cannot be done by him.
8.Where can (could) they have gone to? 他们会去哪儿了呢?
9.He can´t (couldn´t) be over sixty. 他不可能超过六十岁。
10.How can you be so careless? 你怎么这么粗心?