情态动词 The Modal Verbs
 情态动词本身有词义，表示说话人的语气或
者情态，但词义不完全，不能单独作谓语动
词，一般只能与动词原形一起构成谓语。
情态动词
1. 有的情态助动词
有现在时和过去时
两种形式。
 有的有现在时而无
过去时。
 有的有过去时而无
现在时。

现在时
may
can
must
ought to
will
shall
need
dare
--
过去时
might
could
(had to)
-would
should
-dared
used to
情态动词
 2.
情态助动词的推测性用法与非推测性用法
推测性意义是情态意义的重要组成部分，指的是
说话者的某种假设、猜测，对可能性程度的估计，
能表示不同程度的推测性意义，例如：
A. Where is Jack?
B. He is in his room. (100% sure) (无情态动词)
情态动词
He is in his room. (100% sure) (无情态动词)
He might be in his room. (about 30% sure)
He may/should/ought to/would/will be in his
room. (less than 50% sure)
He must be in his room. (95% sure)
其中might所表示的可能性或肯定性程度最低，
must 最强，表示说话者对所陈述的事情充满信
心。might与must都是表示现在，只是程度不同。
情态动词
He might be in his room yesterday. 是错句。
对过去行为的推测应该用：
He may / might have been in his room
yesterday.
情态动词
情态动词的非推测性意义包括所有推测性意义以
外的意义，大多数情态动词都具有一词多义的特
征。
May I come in?（允许）
Can I use your dictionary for a moment?（允许）
She can speak three foreign languages.（能力）
Won’t you come over here?（意愿）（好吗？）
情态动词
I should have told you the news last night. （应该）
You ought to be polite to the lady. (应该)
We must work harder. （必须）
情态动词非推测性意义与情态动词的主语有关。
（而不是与说话者有关）一词多义。
情态动词的推测性意义与说话者有关。不同的情
态动词能表示不同程度的推测意义。
情态动词
 3.
can, could
Some of us can use the computer now, but
we couldn’t ten years ago. （能力）
You can go now.（许可）
He said I could borrow his bike.（许可）
At that time I thought the story could not be
true.（可能）
What on earth can this mean?（惊异）
Could you wait a few days for the money?
（用could代替can,语气婉转）
情态动词
can和be able to都可以表示能力，意义上没有
区别，但是can只有过去式could,而be able to
又更多形式。
No one is able to do it. (No one can do it.)
We shall be able to finish the work next
week.
I haven’t been able to find the book.
情态动词
could, be able to都可以表示能力，但表示过去
能做某一件事而且做成了，则不能用could，而
要用was/were able to, 相当于managed to do,
succeeded in doing.
I was able to run away, but Tom wasn’t.
He ran as fast as he could. In the end, he
was able to arrive in the city in time.
情态动词
could have done / can have done
1. 表示过去的可能性
He is so forgetful that he could easily have
forgotten all about it.
2. 在否定句或疑问句中，表示对过去发生的事情
有怀疑或不相信。
He couldn’t have done such a thing.
Can he have written the book alone?
3. 表示过去能做而未作的事情。
I could have come earlier! 我本可以早点来的啊！
情态动词
 4.
may might
1. 表示允许或者征询对方许可，有“可以”的意
思（否定may not）但在表示“不可以”、“禁
止”、“阻止”的时候，常用must not
You may go now.
He said that I might borrow his bike.
May I watch TV after supper? Yes, you may. / No,
you mustn’t. / No, you’d better not.
Might I use your telephone?(比may更礼貌)
情态动词
2. 表示可能性时，用might语气更加不肯定。
He may be right. / He might be right.
She may come today. / She might come today.
may / might have done对过去行为的推测表示
“想必”、“也许是”
Alice might have gone to bed because there is
no light in her room.
He might not have finished his homework.
情态动词
3. 表示祝愿等，虚拟语气
May our friendship last forever!
May you succeed!
情态动词
 5.
must, have to 和 ought to
1. must表示“必须” mustn’t 表示“不允
许”“不准”“禁止”
Everybody must obey the rules.
The work must be finished as soon as possible.
You mustn’t lend it to others.
You mustn’t speak like that to your mother.
--Must I be home before 8 o’clock?
--Yes, you must. No, you needn’t. No, you don’t
have to.
情态动词
2. must 表示推测（“一定”“必定”），只用在
肯定句中。
You must be hungry after the long walk.
Must have + pp. 只表示对过去某事的肯定推测。
（一定做了某事）
I didn’t hear the phone. I must have been
asleep.
表示否定则用needn’t have + pp. (本来不必)
You needn’t have bought the book.
你本不必买这本书。
情态动词
注意：must 表示猜测时，其反义疑问句要根据表
达者所猜测的时间来决定反义疑问句的时态。
He must have been to Shanghai, hasn’t he?
You must have come to school yesterday,
didn’t you?
He must be our teacher’s son, isn’t he?
情态动词
3. must 是说话人的主观想法，而have to却是客观
需要，具有更多形式。
I must go now. （主观看法）
I have to go now. （客观需要）
You don’t have to worry about it.
He had to spend his childhood in hardwork,
helping his father on their farm.
The students of today will have to know how
to use the computers of tomorrow.
情态动词
4. ought to 表示应该做某事（口气比should重）
You ought to follow your father’s advice.
情态动词
 6.
need, dare
作情态动词用于否定句、疑问句中，dare还可以
用于条件从句中。(need + v原)
He needn’t pay for it.
Need you go now? yes, I must. No, I needn’t.
How dare you say I’m unfair?
Dare she go home alone at night?
She dare not do so.
If the enemy dare invade us, we will certainly
wipe them out.
如果敌人胆敢侵犯我们，我们定将把他们歼灭。
情态动词
Need, dare 也可以用作行为动词
Need to do, dare to do
We need to think it over.
Does he need to know that?
She didn’t need to go.
Who dares to go?
I don’t dare to ask her.
Does anybody need to see the doctor?
情态动词
 7.
shall, should
1. shall 作为情态动词，用于第二第三人称表示说
话的人的意愿，有“命令”“警告”“强制”之
意。
You shall do as I say. 你得按我说的做。
（你并不愿意，而是说话人要求这样做。）
This boy shall go to school next summer.
（这个孩子并不愿意，是说话者要求他上学。）
（比较：The boy will go to school next summer.
本人愿意上学。）
Tell him that he shall buy the book tomorrow.
告诉他，明天他得买这本书。
情态动词
2. 在疑问句中用来征询对方意见，用于第一第三人
称。
Where shall I wait for you?
Shall he come at once?
Shall we start the meeting now?
情态动词
3. should 表示“劝告”“建议”时，可译作“应
该”。
You should keep your promise.
We should be strict in all our work.
情态动词
4. should have +pp. 表示过去应该做而没有做某
事。Ought to have + pp. （语气更强烈）
You should have come earlier.
I regretted the days when I had played and
should have studied.
You shouldn’t have made so many mistakes in
your homework.
You ought to have finished the task.
情态动词
 8.
will would
1. will 表示“意志”“意愿”，可用于各种人称
I will tell you all about it.
We’ll help him if he asks us.
He won’t go. 他不愿意去。
情态动词
2. will 在疑问句中用于第二人称时，表示询问对方
的意愿或者向对方提出请求。
I’m going to the shop after school. Will you go
with me?
Wil you please give him a message when you
see him?
Won’t you sit down?
情态动词
3. 表示习惯性动作，有“总是”“惯于”的意思。
Fish will die out of water.
He will take for hours if you give him the
chance.
Some birds will fly away to the south when the
weather turns cold.
情态动词
4. would 是will的过去式，表示过去时间的“意
志”“愿望”，用于各种人称。
They said that they would help us.
I promised that I would do my best.
情态动词
5. would用于第二人称作主语的疑问句，表示对对
方的请求，语气比will婉转，指现在时间。
Would(will) you be so kind as to tell me the
way to the station?
Would you like some bananas?
Would you like to see a film? Yes, I’d like to.
Thanks. I’m afraid I won’t be able to.
口语中，I would like to 与 I should like to相同。
Like 也可以是love
情态动词
6. 表示过去的习惯动作。
She would sit like that for hours.
Every day he would get up at six o’clock and
light the fire.
情态动词
 9.
used to
1. 表示过去，现在已不复存在
When I was young, I used to take cold baths.
He used to be an army officer.
He used to walk miles after supper.
情态动词
2. 在疑问句或者否定陈述句中，可以有两种形式。
Used you to go to school in the U.S.?
Did you use to go to school in the U.S.?
I usedn’t to smoke.
I didn’t use to smoke.