情态动词
情态动词表示说话人对某一动作或状态的态度，可以表示“可能”、“可以”、“需要”、“必须”或“应当”等之意。情态动词没有人称和数的变化。但不能单独作谓语动词用，必须和不带to 的不定式连用构成谓语动词。只有情态动词ought要和带to的动词不定式连用，在句中作谓语用。
一．can/ be able to
can 表客观的能力，be able to表通过主观的努力，能够……
eg. He is a native speaker of English, so he can speak English well.
The fire was big, but he was able to escape.
二．shall 用于二、三人称表命令，警告，威胁。宣布法律，法规时用shall.
eg. The judge declared that all the money shall belong to the wife.
—What does the sign over there read?
—“No person smoke or carry a lighted cigarette，cigar or pipe in this area.”
A.will
B.may
C.shall
D.must
三．1. should 表推测时指确定或期望，即合乎理想的情况或结果。
It’s nearly seven o’clock. Jack should be here at any moment.
2. should 表“竟然”
How should he do like this?
四. 情态动词表推测。
1. must may might 用于肯定句，语气减弱。
can’t couldn’t 意为“不可能”，用于否定句，疑问句。
不存在mustn’t have done
eg. He must be at home.
He may go out .
He can’t be watching Tv.
He couldn’t have finished the job yesterday, for he was badly ill.
2. could have done 本可以……（实际没有）
He could have been admitted to the college, but he failed.
五．1. may 表征求对方意见。
May I have a look at it ?
2．表推测时may 表不确定。
eg. The train might leave at six, but I’m not sure.
3. may /might as well 不妨……，不如……
eg. It is dark and you may as well stay here .
Since the flight was cancelled，you might as well go by train.
六．情态动词+ have done
1. should (not) have done
ought (not) to have done 本应该做某事。
eg. You should have come here earlier.
You oughtn’t to have eaten too much.
2. must have done 表示对过去已经发生的行为进行推测，意为“一定做了某事”
eg. It must have rained last night, for the road was quite muddy.
3.may / might have +过去分词，表示对已发生的事情做不肯定、可能性很小的推测，或事实上根本没发生，译为“也许……”。如：
4. couldn’t have done / can’t have done表示对已发生情况的否定推测,“不可能做了某事”eg.Time was limited, so he couldn’t have finished the task.
Mary my letter; otherwise she would have replied before now.
[A] couldn’t have received[B] ought to have received
[C] has received [D] shouldn’t have received
5. needn’t have done “本没有必要做了某事”
eg. You needn’t have taken a taxi here, for it was near to your house.
needn’t do “没必要去做某事”
You needn’t go now.
As it turned out to be a small house party，we so formally.
[A] needn’t dress up [B]did not need have dressed up
[C] did not need dre ss up [D] needn’t have dressed up
七．can’t be too can’t never be too
eg. You cannot be too careful when you drive a car.
八．It couldn’t be better. / It couln’t be worse. (交际用语)
How do you find the restaurant?
It couldn’t be better. / It couln’t be worse.
1. I was really anxious about you. You ______home without a word.
A. mustn’t leave
B. shouldn’t have left
C. couldn’t have left
D. needn’t leave
2. ------Write to me when you get home. ----_________.
A. I must
B. I should
C. I will
D. I can
3. You can’t imagine that a well-behaved gentleman _____ be so rude to a lady.
A. might
B. need
C. should
D. would
4. Mr.Bush is on time for everything. How _____ it be that he was late for the opening ceremony?
A. can
B. should
C. may
D. must
5. He heisitated for a moment before kicking the ball, otherwise he _____ a goal.
A. had scored
B. scored
C. would score
D. would have scored
6. ------I hear you’ve got a set of valuable Australian coins. _____ I have a look?
-----Yes, certainly.
A. Do
B. May
C. Will
D. Should
7. -----Is John coming by train?
-----He should, but he ______not. He likes driving his car.
A. must
B. can
C. need
D. may
8. It has been announced that candidates _____remain in their seats until all the papers have been collected.
A. can
B. will
C. may
D. shall
9. It is hard for me to imagine what I would be doing today if I _____in love at the age of seven, with the Melinda Cox Library in my hometown.
A. wouldn’t have fallen
B. had not fallen
C. should fall
D. were to fall
