情态动词是什么,用法口诀是什么,The meaning of a modal verb is necessary. The meaning of a negative sentence is not necessary. The meaning of a modal verb is that it can only be used in questions and negative sentences. It cannot be used in positive sentences. It needs to be used as a substantive verb。
英语中情态动词有什么
到目前为止，英语中有13个情态动词，所以动词有一定的意义，但到目前为止，它们还不能独立作谓语，只能与动词基形一起构成谓语。
It is possible to do STH. Yes, yes; Will be; Should, should, should; Must, need, dare, habit, should。
·情态动词的语法特征
1)情态动词不能单独做谓语,除应该和有外,后面只能接不带到的不定式。
2)情态动词没有人称,数的变化,但有些情态动词,如可以将也有一般式和过去式的变化。
3) 情态动词的 时态 形式并不是时间区别的主要标志,不少情况下,情态动词的现在式形式和过去式形式都可用来表示现在时间 过去时间和将来时间 情态动词属不及物动词,故没有被动语态。
情态动词的用法口诀：
动词基形后，说话语气委婉“可以”;“能力”may"许可证”,must"责任”;”或““义务”;“不需要”回答“不需要”。“需要，敢”;敢”;should"“应该”;,如果;“希望”;, to"被迫“客观表象”。
can, could 和be able to的用法
1.can, be able to都可表示“能力”
Can的主语是人或物,be able to的主语是人
She can/be able to sing the song in English.
This machine can make you feel comfortable.
2.Only used in the present tense and the past tense (possibly) Can it be used in various tenses。
We’ll be able to finish the work soon.
I haven’t been able to see the film.
could用于表示泛指过去的能力。如：
I could read when I was four.
Though the soldier was badly wounded, could he tell what had happened。
She ran fast but she couldn’t /wasn’t able to catch the bus.
3.表示特定的某一过去能力或表示成功地做了某事时，只能用was/were able to， 不能用could。
He was able to flee Europe before the war broke out.
He was able to swim halfway before he got tired.
4.Can not express the tense, to express a gentle request,(note that the answer can not use energy) is often used to express a request for help from others or elders。
Could I have a look at your notebook?
Yes, you can./No, you can't.
(在否定回答时要注意:在拒绝长辈的要求时，不能用“can not”，这样太生硬无礼，但在拒绝长辈的要求时可以用“can not”)。
5.表示惊讶、怀疑或不相信的(主要用于否定句、疑问句和感叹句)。
Can this news be true?
How can you be so foolish?
It can’t be Mary. She has fallen ill.
6.可能，可能，可能，可能，可能，可能，可能，可能，可能，可能，可能，可能，可能，可能。不可能”;)和问题;could既可以用在肯定句中，也可以用在否定句和疑问句中。也许然后;可能是”;)。
Linda didn’t catch the train. She could have caught it.
Don't worry. They could have just forgotten to phone.
may和might
1.May and may are used in general questions to express a euphemistic request, positive answer with may, negative answer with can't。
---May I use your pencil?
---Yes, you may./ No, you mustn’t.
2. may和might表示“可能性”, may/might + v 指现在或将来可能发生的动作情况。might暗示的可能性更小
She may not be working now. John might be at home now.
3.对过去发生的事情的可能性作出判断用may/might have done,用might比用may的可能性更小
She may/might have gone to the cinema.
They may/might not have received our telephone.
4.may 放在句首祈使句，表示祝愿。
May you succeed! May God bless you!
Will 和 would
1.will和would表示意愿、意志，可用于各种人称
If you will help me with my English, I will be very happy.
I promised that I would do my best.
2.在疑问句中，will用第二人称来询问或寻求建议。会更委婉些吗。
Will you tell him the news as soon as he comes back?
Would you please speak again more slowly?
shall ,should 和ought to
1.shall用于第二、三人称表示允诺、警告、命令、决心等。
You shall do as I say. (命令)
Tell him that he shall have the book tomorrow. (允诺)
Nothing shall stop me doing it. (决心)
2.在疑问句中，用第一第三人称询问或征求意见。
Shall I open the window for you?(征求意见)
Shall he fetch some water for you?(请求)
3.Should often express advice, advice and command, and should have similar meaning, but should express responsibility and obligation, strong tone in questions generally used should instead of should。
Young people should learn how to use computers. Every citizen should obey the law. Shouldn't you go。
4.should/ought to have done表示责备或批评,意为“本应该做到…但没有做到…”,用于否定则表示“本不该…但”ought to的语气更强烈.
You should/ought to have told her the truth earlier.
She shouldn’t have left without saying a word.
must 和have to
1.Must be used in general questions, affirmative answer must be negative t or do not need, do not need, do not, must t is forbidden, not allowed。
— Must I finish all assignments at a time?
—Yes, you must.
No, you needn't.
You mustn’t get down while the car is still moving.
2.“must”和“have to”之间有细微的区别。must强调主观观点。have to强调客观需求。
I don't like this TV set We must buy a new one There are no buses any more They have to walk home。
3.Have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have to have done。
You must be the new teacher.
He must be joking There's no one here they must all have gone home。
4. Must表示“偏要，硬要”，指做令人不快的事情
While she was busy cooking, he insisted on asking questions. Of course, after I gave her advice, she had to do the opposite。
情态动词的特点是什么
情态动词没有人称和数的屈折变化。动词后接情态动词必须是原形。否定形式是情态动词的“add”。not"有些情态动词有现在时和过去时。过去时用来表达一种更礼貌、委婉的语气。它的时态不强。
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。
基本助动词和情态助动词的一个主要区别是，基本助动词没有自己的意思，而情态助动词有自己的意思，可以表达说话人对动作或状态的看法，也可以表达主观的假设。
What have you been doing since? （构成完成进行体，本身无词义）
你一直在干什么？
I am afraid I must be going. （一定要）
恐怕我必须走了
You may have read about it (or may have)。
你可能已经看到了一些相关报道。
此外，情态助动词还具有以下词汇和句法特征。
如果我们认为ought to和used to是固定短语，那么所有情态动词，无一例外都只能跟在不带to的不定式后面。
We used to grow beautiful roses We used to grow these beautiful roses。
I asked him if he would come and fix my TV set。
情态助动词在有限动词短语中总是排在前面。
They need not have been punished so severely.
他们不需要这么严厉的惩罚。
情态助动词用第三人称单数现在时，不加变位，即不加-s形式。
She dare not say what she thinks.
她不敢说她是怎么想的
情态动词没有有限形式，即没有不定式或分词形式，也没有相应的动名词。
Still,she needn't have run away.
不过，她不必跑了
在很多情况下，情态助动词的现在时和过去时可以表示现在、过去或将来的时间。
Would you mind very much if I ask you to do something?
你真的介意我请你做件事吗。
She told him he ought not to have done it.
她告诉他不应该这么做。
情态助动词是互斥的，也就是说，在有限动词中。
一个词组中只能出现一个情态助动词，但有时它可以与基本助动词have和be连用。
You should have washed the wound.
你应该已经洗好了伤口
Well,you shouldn't be reading a novel.
你不应该看小说。
我们不必去不必去。
Must I read books every day、我必须每天读书
No,you needn't . 不，你不必
什么是情态动词
情态动词本身具有一定的意义，用来表达语气的词却不能独立作为谓语，只能与动词基构成的情态动词一起构成谓语动词用在动作动词前面，用来表达说话人对动作或状态的看法或主观假设的情态动词虽然数量不多，但被广泛使用。
它们主要如下:can(可能)，may(可能)，must(必须)，need(需要)，ought to(应该)，dare(敢)，shall(应该)，will(会)。
need情态动词和实义动词有什么区别
1、本质特征不同
1)需要作为情态动词,具有情态动词的共同特征。
need+动词原形
人数和时态没有变化。
need+not构成否定
need放句首构成疑问句
2)需要虽为情态动词,但具有与其他情态动词不同的特点。
need作为情态动词，只能用于疑问句和否定句，不能用于肯定句。
3)需要作为实义动词,具有实义动词的共同特征。
人称数和时态有变化。
需借助do,does,did,will等构成否定或疑问
2、词义不同
我不需要。我不需要。我需要它。作为一个实用动词，need的意思是需要。
3、句型结构不同
1）need做情态动词：
needn't do sth. 不需要做某事
needn't have done.用于对过去的责备，表示"没有必要做某事，可是做了"。
2）need做实义动词：
need sth./sb. 需要某物/某人
somebody need to do.某人需要做某事
something need doing 某事需要被做
something need to be done 某事需要被做
need somebody to do something 需要某人做某事
情态动词是什么
大多数情态动词的时态较弱，可以用在过去式，现在式或将来式但也有独立的情态动词，有现在式和过去式常用情态动词有can (could)，may (might) must need ought to dare (dare) shall (should) will (would)。
像need、dare、have to、be able这样的短语通常被称为半情态动词，与can、could、may、might和must这样的情态动词相对。
“need”和“dare”既可以用作情态动词，也可以用作实义动词，而“have to”和“be able to”等短语在意义和语气上与情态动词相似，也包括在情态动词用法中。
