第九节情态动词
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第九节情态动词
第九节情态动词
一.情态动词的类型与特征
1. 情态动词的类型
只作情态动词的有：must, can/could, may/might
既可作情态动词也可作实意动词的有：need, dare
可作情态动词也可作助动词的有：will/ would, shall/should
具有情态动词的某些特征的有：have to, ought to
2. 情态动词的特征
有一定的意义，表示说话人的语气和情态；无人称和数的变化，不能单独做谓语动词，要和行为动词和系动词连用才能构成谓语；后面跟动词原形；具有助动词的作用，可用了构成否定句，疑问句，以及用于简单答语。
They must start at once.
He has to stay inside now.
She may lose her way.
-Can you speak English? –Yes, I can.
二. 情态动词的用法
1. 用于表示交际的情态动词
（1）用will, would, can, could表示请求，请别人做某事
will/would you please do……？
can/could you……？
注意：使用would, could比will, can 更正式，委婉，客气。
（2）用can, could, may, might询问是否许可
can/could I do……？
may/might I do……？
注意：使用could, might比can, may更正式，委婉，客气。
-Could/can I use your computer?
-Yes, of course, you can. (回答时不能用could) -Might/may I have a look at your new room?
-Yes, you can. （回答时不能用might）
（3）shall用于第一人称和第三人称疑问句，表自己想做，要求对方做决定，征询对方意见
shall I/we/he/she/they……？要不要……？
The room is so dirty. Shall we clean it?
Shall these goods be sent to you at once?
（4）had better/ should/ ought to/ must可以表示规劝，建议，“最好，应该，必须”表示“最好”用had better, 其否定式为had
better not
You had better get up early.
表示“有义务”或“有必要”，要用should或ought to, ―应该‖，其否定形式为shouldn’t或ought not to，“不应该”
You should brush your teeth before you go to bed.
表示“必须”用must，其否定式为mustn’t，“不许”
The teacher said all the students must hand in the homework.
注意：had better—should—must 语气逐渐加强
2. 用于表示推测的情态动词
（1）根据某一事实，现象推测可能发生的情况，可用must，may，might，其中must把握性最大，might把握性最小
must表示对事物的推测时，意思为“想必，一定”，只用于肯定句中；表示有把握的否定判断时用can’t，意思为“不可能”
You must be tired. Go and have a rest.
It can’t be Mr. li. he has gone home.
may和might表示说话人的猜测和对可能性的判断，意思为“可能，也许”，否定式为may not和might not.
If you are not careful, a car might hit you.
--Where’s William? –He might be in the classroom.
(2)can表猜测时译为“可能”，常用于否定句和疑问句中。
She can’t be hungry. She has just had lunch. -Can it be the headmaster?-No, he has gone to Beijing.
(3)根据经验或惯例对某一情况进行推测，用should或ought to，“按理应该”It’s nearly seven o’clock. Jack should be here at
any moment.
3. 必须区别或注意的情态动词
（1）can与be able to
can可以表示“具有某种能力”，“能，会”，与be able to的意义基本相同。但can 只有一般现在式和一般过去式，而be able to却能用于各种时态。
Tom c an’t (isn’t able to) come because he is ill.
No one could (was able to) answer the question.
He has not been able to get there before dark.
注意：be able to的过去时was/were able to可作“设法做成某事”，相当于manage to do sth或succeed in doing sth,而can的过去式could没有这个含义。
With the help of firemen, they were able to leave the burning
house.
(2)need和dare的用法
need和dare作情态动词时，没有人称变化，多用于否定句，疑问句或条件句中。You needn’t study so hard.
-Need I go at once? –No, you needn’t.
Mary dare not touch the snake.
need和dare作实意动词时，可用于肯定句，否定句，疑问句中，有词形变化，可加助动词，其后可接名词，代词，动词-ing，或带to的动词不定式，I dare say 为固定结构，不加to.
We’ve got enough coffee. We don’t need any more.
She needs three people to bring the food.
Do you dare to answer the questions openly?
I wonder how he dares to say so.
（3）must和have to的用法 must表示说话人的主观思想，强调个人意志和主观决定，多用于一般现在时，用于否定句中意为“不许，禁止”，have to侧重客观上的必要，不得不，强调客观条件作用的结果，可用于多种时态，用于否定句中表示“不需要”。
You must do it now. You mustn’t go there.
I have to go now.
巧计have to和must
“主观责任”说“必须”，must赶紧用上去；要是“环境”“不得不”，赶紧换用have to
衔接训练
1. –Must we do our homework first?
--No, you _____. You may have a rest first.
A. mustn’t
B. needn’t
C. may not
D. can’t
2. --______ I take the newspaper away? –No, you mustn’t.
You ______ read it only here.
A. Must, can
B. May, can
C. Need, must
D. Must, must
3. If you got lost, you ____ ask that man over there. Maybe he
knows the way.
A. had better not to
B. had not better
C. had better
D. had better not
4. Even the top students in our class can’t work out this
problem, so it ____ be very difficult. A. may
B. must
C. can
D. need
5. –He ____ be in the classroom, I think.
--No, he ___ be in the classroom. I saw him make his way
home a minute ago.
A. can, may not
B. must, may not
C. may, can’t
D. may, mustn’t
6. You ___ go and see a doctor at once because you’ve got
a fever. you need to get medical treatment.
A. can
B. must
C. dare
D. would
7. In order to save energy, you _____ turn off the light when
you leave the room.
A. ought to
B. ought not to
C. has to
D. may
8. He said he would rather not ______ it right now. He made
up his mind to look for a better solution.
A. doing
B. to do
C. do
D. to be doing
9. I thought you _____ like something to read, so I have
