英语语法 情态动词

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情态动词
情态动词是高考的重点考查项目，对学习情态动词的要求是：
首先、了解情态动词各自的基本意义及用法，然后掌握情态动词表示推测的用法（其中重点是对表过去推测的用法）还要注意带有情态动词的反意疑问句的用法。

情态动词的特征：
1.本身有词义，但完全。因此不能独立作谓语，只能和动词原形一起构成谓语。
2.后接动词不定式一律不带to
3.不随人称和数的变化。

情态动词各自的基本意义及用法
表一、can 与could用法对比表
对比点 can could
1、表“能力” Can you lift this heavy box? I couldn’t understand what he said at all.
2、表“许可” You can use a different material instead. He said I could borrow his bike.
3、“怀疑” No, no, it can’t be true.
What on earth can this mean? We thought the story could not be true. How could you be so careless?
4、can与be able to 区别 1. could代替 can，表示语气更为婉转。
Eg. Could I use your bike? Yes, I can 

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2. can (能够)=be able to(仅表能力时)，但be able to 表示一番努力后，才能做得到，且有更多的时态。
He was a good swimmer, so he __________ swim to the river bank when the boat sank.
A. could B. might C. shall D. was able to

表二、may与 might用法对比表
对比点 may Might
1．表“询问” May I …?(=Can I …?) Might I …?(=Could I…?)(但比用may 更客气)
2.表“允许” You may take the boy there. He told me he might come .(might 与told相呼应)
3．表“可能”“或许” She may nor like this place. I’m afraid he might not like this play.
注： 1. May I…?的答语。
2.may可表示期望或祝愿
May you succeed !
3.may (might)用于目的状语从句中 肯定：Yes, you may.
否定：No, you mustn’t 不行（语气强硬）
No, you may not 或No, you’d better not.
The emperor gave them some gold in order that they might begin their work at once.
表三、must与have to的用法对比表
对比点 must have to 
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1．表“必须” （主观看法）必须；没有过去式，可用于间接引语中。He told me I must do according to what he said. （客观需要）不得不，有多种时态。It’s raining heavily, we can’t go now.
2.疑问句 Must I …?
Yes, you must.（一定）
No, you needn’t./ you don’t have to.(不必) Do you have to go today?
Yes, we do.
否定句：You don’t have to worry about that.

表四、need与dare的用法对比表
对比点 need dare
1.情态动词+动词原形
1）否定式
2）疑问式 He need not (needn’t)go.
----Need we do it again?
---No, you needn’t do it again. He dare not say so.
Dare she go out alone at night?
How dare you say I’m unfair?
If he dare do that, he’ll be punished.(条件句)
I dare say.(固定用法)
2.行为动词+带to不定式 
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1）肯定式
2）否定式
3）疑问式 He needs to go.
He doesn’t (does not)need to go.
Does he need to do it again?
No, he doesn’t need ot do it again. He dares to say.
He does not(doesn’t)dare to say.
If you dare to jump into the water from here, so dare I .
3. did not need to do
表示过去没有必要做 She didn’t need to attend the meeting yesterday, and she stayed with her children.(她没有参加)

表五、should与ought to用法对比表

对比点 should ought to
1、表“应该” 表劝告、建议
You should listen to the doctor’s advice.
We should learn from Zhang Hua 表示“有责任有必要”做某事
You ought to finish your work before you go home.
We ought to help each other. 
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2、表“估计”

They should get home by now. 表示“非常可能”的事，可译为“总应该”
If we start to work right now, we ought to finish it before lunch.(午饭前应当能干完)

注： 1）、should还可在虚拟语气中的使用
2). 注意：ought to的疑问式及否定式
----Ought he to go? ----Yes, I think he ought to.
No, he oughtn’t to.
否定式：ought not to a或oughtn’t to do(不说ought to not do)
反疑问句：oughtn’t ______?

表六、shall与will的用法对比表
shall Will
1. 征询对方意见或请求指示，用于第一、三人称：
Shall I (we)…?
Shall he (she)…?
Where shall I (we)wait for you? 1． 询问对方的意思或向对方提出要求：
Will you(please)…? Won’t you…?
Would you like to…?(用would替代will更客气) 
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----Won’t you go and see the film?你不去看电影吗？---Yes, I think I will. 不， 我想去。

2. 表示说话人的“意愿”有“命令”“警告”“强制”“允诺”“决心”等，用于第二、三人称，要重读。
You shall do what I tell you ( to do).
我叫你干什么你就干什么。
Everything shall be done to save the ship.
一定要竭尽全力来拯救这艘船。 表示“意志”“意愿”，用于各种人称：
I won’t do anything you don’t like.
我不会做任何你不喜欢的事。
Would表示过去时间的“意志”“意愿”
Shylock would not take the money earlier.
夏洛克先前是不肯要钱的。

表七：used to与would用法对比表
used to would
1.表示过去的动作、状态，重在与现在情况的对比，不一定要有时间状语。
I used to play cards a lot, but now I seldom play.
My hometown is not what it used to be. 1.只表示过去动作的重复，有明确的时间状语
I would go to see my grandfather on Sunday when he was in the middle school.
2.would 后只接表动作的动词，不接表认识或状态动词
He used to be nervous in the exam. 
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2.表示过去的习惯有时可互换：
When we were very young, we used to / would go skating every winter.
2. 表示过去的次数时，不能使用：
( √）We went to the Great Wall five times when we were young.
( X ) We used to go / would go to the Great Wall five times when we were young.
注：used to do的否定式：usedn’t to do 或didn’t use to do (usedn’t也可写作usen’t)
疑问式： Did you use to do ? Didn’t you use to do?
Used you to do? Usedn’t you to do?

情态动词表推测
情态动词表推测的意义：
1、大多数情态动词（除表‘能力、许可、意志’外），都可以表示推测，其程度有差异。按其可能性程度的高低排列为：
Must ﹥will ﹥would ﹥ought to ﹥ should ﹥ can ﹥ could﹥ may ﹥ might
肯定 完全可能 很可能 可能 有可能
2.注意区分情态动词的否定的含义：
may not或许不、可能不 might not可能不 can’t 不可能
mustn’t不许、禁止 shouldn’t不应该 needn’t 不必
3.情态动词表推测具体运用：情态动词可以对现在、进行、过去推测 

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S主+情态动词+be+adj 对“性质”“特征”的推测
S主+情态动词+be+n 对“职业”“事物”的推测

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英语语法 情态动词