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英语必修三语法：情态动词情态助动词有十三个：
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。
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.
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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）。
Could I have a look at your notebook?
Yes, you can./No, you can't.
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.
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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“必须”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”，“一定” ，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。
英语必修三倒装知识点讲解1.在there be/live/lie句型中用全部倒装;
2.在以there, here, now, then +be/come/go+主语的句子中用全部倒装;
注：如果主语是代词则不用倒装。
3.以off, away, out, in, up, down等副词开头的句子以示强调或为了使情景更生动，句子用全部倒装;
注：如果主语是代词则不用倒装。
4. only, not until所修饰的介词短语、副词或状语从句放在句首时，要部分倒装;
注：①主句倒装，从句不倒装。
②Only+主语置于句首时，不倒装。
5. never, hardly, seldom, scarcely, barely, not, few, little, often, by no means, at no time等放在句首时，要部分倒装;
6.在no sooner…than; not only…but also; hardly/scarcely …when; 句型中，前面的句子要部分倒装;
注：not only…but also, neither…nor连接两个主语不倒装。
7.以so, neither, nor开头的句子，表相同概念的肯定或否定时，要全部倒装;
e.g.:
I have never been to Beijing. Nor has he.
She is a teacher, so am I.
8.so/such…that句型中，把so/such修饰的那部分放在句首时，主句要部分倒装;
9.as引导的让步状语从句，常把表语、状语置于主首，用倒装;
注：如果表语是单数可数名词，该词前一般不加冠词。
Child as he is, he knows a lot.
10.省略if的虚拟条件句置于句首时，用倒装;
11. Such作表语放在句首时，表示强调，用倒装;
12. 为了保持句子平衡，或使上下文连接更紧，可把介词短语、形容词短语、副词或分词提到主语前，用全部倒装语序。
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