英语中的情态动词是考试会考的一个知识点，那么在英语中情态动词一共有多少个呢?关于情态动词的用法又是怎样的呢?请看下面的英语情态动词及用法大全。

　　情态动词(Modal verbs)本身有的词义，但是不能独立作谓语，只能和动词原形一起构成谓语。英语中的情态动词有十三个：

　　may, might; can, could; will, would; shall, should; must, need, dare, used to, ought to.

　　·情态动词的语法特征

　　1) 情态动词 不能单独做谓语，除ought 和have 外，后面只能接不带to 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can、will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：

　　动词原形接后面，说话语气较委婉。can "能力"may"许可"，must"责任"或"义务"，否定回答needn’t换。"需要"need, dare"敢"。should"应该"，would"愿"，have to"被迫"表客观。

　　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.can只用于现在式和过去式(could)。be able to可以用于各种时态。

　　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.

　　Although the soldier was badly wounded, he was able to 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.could不表示时态 ,表示委婉的请求，(注意在回答中不可用could)常用来表示请求别人帮助或对长辈的请求。

　　Could I have a look at your notebook?

　　Yes, you can./No, you can't.

　　(在作否定回答时，要注意：在拒绝长辈的请求时，不能用can not，这样显得语气太过生硬，不礼貌。但是在长辈拒绝晚辈的请求是可以用can not的。)

　　5.表示“惊异,怀疑,不相信”的态度(主要用于否定句,疑问句和感叹句中)

　　Can this news be true?

　　How can you be so foolish?

　　It can’t be Mary. She has fallen ill.

　　6.表示推测，译为“可能、或许”，can常用于否定句(意思是"不可能已经")和疑问句;could除用于否定句及疑问句外,还可用于肯定句(意思是"那时可能;本来可以")。

　　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和might 用于一般问句中表示委婉的请求,肯定回答用may,否定用mustn’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用于第二人称,表示请求或征求意见,would则语气更委婉

　　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,用于第一、三人称，用来表示请求或征求意见。

　　Shall I open the window for you?(征求意见)

　　Shall he fetch some water for you?(请求)

　　3. should常表示劝告、建议、命令，与ought to意义相近，但ought to多表示责任、义务，语气强烈。在疑问句中通常用should代替ought to。

　　Young people should learn how to use computers. Every citizen ought to obey law. You ought not to 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用于一般问句中,肯定回答用must否定式用 needn’t或don’t have to，做 “不必”,mustn’t表示“禁止，不允许”

　　— 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.表示“需要”这个意思时，must 和have to 稍有区别。must着重说明主观看法，have to 强调客观需要。另外，have to 能用于更多时态。

　　I don’t like this TV set. We must buy a new one. There was no more bus. They had to walk home.

　　3.must表示对某人某事的猜测， 作“准是”，“” ，一般用于肯定句中。对过去发生的事情作肯定判断用must have done

　　You must be the new teacher.

　　He must be joking. There is nobody here. They must have all gone home.

　　4. Must表示“偏要，硬要”，指做令人不快的事情

　　He must come and worry her with question, just when she was busy cooking the dinner. Of course，after I gave her my advice，she must go and do the opposite。