Grammar
情态动词用法
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。
只作情态动词的 can / could, may /
might, ought to, must
可情态可实义的　 need, dare
可情态可助动词的 shall / should, will /
would
相当于情态动词的 have to, had better
1) can的主要用法是：
  A.  表示体力或脑力的能力：
  eg. The girl can dance very well.
B.  表示说话的推测﹑事物的可能性等:
eg. Can the news be true?
C. 在口语中, can可以表示请求或允许:
eg. Can I sit here?
can 和could：
can表示“能够”时与短语be able to同义，但can只用于一般现在时或过去时，而后者可用于各种时态。另外，can表示个人有某种能力，而be able to表示某人通过努力、克服困难做成某事，相当于succeed in doing sth.；叙述过去事实时，最好用was / were able to，因为could只表示过去具有某种能力。
如：
Can you understand the different kinds of English these people are using?
Two years later, he was able to speak very good Chinese.
2) could的主要用法是：
A. could 是can的过去式, 表示与过去 有关的能力和推测:
e.g. We all knew that the young man
couldn’t be a doctor.
B. could可以代替can表示请求, 但语气较can客气、委婉:
e.g. Could you lend me your
dictionary?
Could I use your bike?
3) can和could接动词的完成形式，表示可能已经做某事。can用在否定和疑问句中, 表示不相信、怀疑等态度。
　 e.g. They can't have gone out because the light is still on.
以could或would提问时，不能再以could或would作答，而应该用can或will。如：
—Could I borrow your dictionary?
—Yes, of course you can.
may 和might ：
may 常用来表示：
 A. 表示请求、允许; 比can较为正式:
   e.g. May I come in ?
You may go now.
B. 表示说话人的猜测: “也许” “可能”: 通常只用于肯定句和否定句中。
e.g. --I believe the man is from England.
--But I may be wrong.
The guest may arrive this afternoon.
在肯定句中，may的可能性比can 高，may表示现实的可能性，can表示理论上的可能性。如：
The road may be blocked.
这条路可能不通了。
The road can be blocked.
这条路可能会是不通的。
在疑问句中，表示可能性用can。
如：Where can he be? 他会在哪呢？
C. 表示祝愿;但语气较正式:
e.g. May you succeed!
May you have a good journey!
might 的用法有:
多在间接引语中表示过去的可能和允许。如:
She said that he might take her bike.
她说他可以拿她的自行车去用。
除了在间接引语中以外，might 一般不表示过去的可能或者许可。如要表示过去的可能可以用could, 表示过去的许可可以用was (were) allowed to 或者had permission to 。
表示现在的可能，其可能性要比may 小。如：
She might go home tomorrow.
说不定他明天会回家。
表示现在的许可, 语气比may较委婉, 一般用于疑问句(包括间接疑问句), 不可用于肯定句或者否定句。
如: Might I have a word with you?
我可以和你说句话吗？
will和would：
1. will是助动词或是情态动词？
will用于构成将来时是助动词。用于表示“意志”“决心”“请求”是情态动词。would亦同理。
e.g. I will tell you something
important.
我要告诉你一些重要的事。
（助动词）
Will you tell her that I'm here?
请您告诉她说我在这儿，好吗？
（情态动词）  
2. 在疑问句中用于第二人称，提出请求或询问。
e.g.: If you want help - let me know,
will you?
如果你需要帮助, 让我知道, 好吗?
Will you type this, please?
请打印这个, 好吗？  
Won't you sit down?
请坐下, 好吗？
3. would比will客气委婉。
e.g.: Would you help us, please?
请您帮助我们，好吗？
（表请求）
I’d go there with you.
我要和你一块到那儿去。 
Teacher wouldn’t allow it.
老师不会允许这件事。
（表意愿）
（表许可）
shall和should：
1. shall用于构成将来时是助动词。
shall用于征求对方的意见，表示 “决心” 是情态动词。
e.g.: Perhaps I shall pay a visit to
England this winter.
可能今年冬天我会去英国观光。
（构成一般将来时, 助动词）
Shall we go by train, Mom?
妈妈，我们乘火车去好吗？
（用于征求对方的意见，情态动词）
I shall go at once.
我必须立即去。
（表 “决心”，情态动词）
shall可以用于第一、三人称的疑问句，表示征求意见或许可；还可用于第二、三人称的陈述句中，表示允诺、警告、命令或威胁等。如：
You shall be punished if you break the rule.
2. should表示义务、建议、劝告，意为 “应该”。 “should+ have+过去分词”
表示本应该在过去做但没有做。
eg: You should keep your promise.
你应该遵守诺言。
She should have passed the exam.
她应该通过考试的。
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.
I don’t like this TV set. We must buy a new one. There was no more bus. They had to walk home.
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。
You must be the new teacher.  
He must be joking. There is nobody here. They must have all gone 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
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.
4. must表示“偏要, 硬要”, 指做令人不快的事情
can / could, may / might, should和must都可表示肯定的推测。can / could表示客观可能性；may表示推测时，其语气不肯定；might语气更弱，表示某事实际发生的可能性；should表示确定或可能有的未来或期待；must表示比较肯定的语气。如：
I think advertisements can be quite dangerous.
The newcomer may be dismissed by the company.
The rescue team should arrive by 5 o’clock this afternoon.
I think the old woman must be a nice person.
could, might, would, should都可表示委婉语气。如:
I wonder if you could let me use your cell phone.
Might I know your telephone number?
2. A: ______ Xiao Feng find the origin of Easter from that book?
B: No, he _____________.
1. A: ______ you like to go to a special event with us on Saturday?
B: Yes, I _____________________ _________.
Would
’d like to go with you on
Saturday
Could
couldn’t find it
Exercise
3. A: _____ I go with my friend to the harvest festival?
B: Yes, you _________________ ________.
4. A: If I want to be a doctor _______ I study science?
B: Yes, you __________________.
should study science
May
may go (with your
should
friends)
5. A: He is very handsome. ____ he play the role of the prince?
B: No, he _______________________ ______.
can’t play the role of the
Can
prince
6. A: The neighbour’ s children are older this year. _______________ they stop playing tricks at Halloween?
B: Perhaps, they __________ ________________________.
__________________________
____________.
Might
or Should
might stop
or should stop playing tricks
playing tricks at Halloween
at Halloween
—I think I’ll give Bob a ring later
in the week.
—You _____. You haven’t been in
touch with him for ages.
A. will B. may
C. have to D. should
D
练习坊
I. Choose the correct answer.
2. John, look at the time. _____ you play
the piano at such a late hour?
A. Must B. Can
C. May D. Should
A
3. There _____ any difficulty about
passing the road test since you have
practiced a lot in the driving school.
A. mustn’t be B. shan’t have
C. shouldn’t be D. needn’t have
C
4. The World Wide Web is sometimes
jokingly called the World Wide Wait
because it ______ be very slow.
A. Should B. must C. will D. can
5. Helen _____ go on the trip with us,
but she isn’t quite sure yet.
A. shall B. must
C. may D. can
D
C
6. —Someone is knocking at the door.
_____ it be Venis?
—No, it _____ be her; she left for
New York this morning.
A. Can; mustn’t
B. Might; can’t
C. May; doesn’t
D. Can; can’t
D
7. Mike promised his doctor he _____
not drink, and he has never drunk
ever since.
A. might B. should
C. could D. would
D
8. —Is there a movie on in the cinema
tonight?
—There _____ be. I will phone the
cinema and find it out.
A. might B. should
C. can D. must
A
9. When I was studying at Beijing
University, I _____ take a walk along
the lake every evening.
A. will B. would
C. could D. shall
B
10. Mr Brown, many students want to
see you. _____ they wait here or
outside?
A. Shall B. Will
C. Can D. Would
A
can; could
When I was young I _____ climb any tree in the forest.
Learning a language _____ be a real challenge.
could
can
II. 选用正确的情态动词填空。
may; might
I asked if I _____ go home half an hour earlier today.
There ____________ not be enough money to pay for the repairs.
might
may / might
will; would
When he got older, he _____ never do his homework.
Nancy _____ keep talking unless you tell her to shut up.
would
will
shall; should
By now, they ______ already be in Dubai.
I _____ be replaced by someone from the New York office.
should
shall
must; can’t
You _____ have stayed up. You look so tired.
You _____ be 45! I thought you were about 25 years old.
must
can’t
Harvest and Thanksgiving festivals can
be very happy events. (P2)
[考点] 情态动词can的用法。
[考例1] It is usually warm in my hometown in March, but it _____ be rather cold sometimes. (福建 2008)
A. must B. can C. should D. would
考点点拨 考例回顾
选B。can表示“可能”，意为“有时天气可能会相当冷”。must必须、肯定；should应该；would表示过去常常。
[考例2] You _____ be hungry already — you had lunch only two hours ago! (浙江 2008)
wouldn’t B. can’t
C. mustn’t D. needn’t
选B。此题考查情态动词表推测。can’t意
为“不可能”；mustn’t意为“禁止、一定不
要”；wouldn’t常表示对现在或将来情况
的虚拟；needn’t意为“没有必要”。