must not/mustn’t do
Must…do…? to.
Yes,…must.
No,…needn’t/don’t have
have to
只好，不得不（客观的必须，有时态和人称的变化）
don’t have to do
Do…have to do…?
Yes,…do.
No,…don’t.
ought to
What would she be doing there?
情态动词+have done的用法
could+have done：本可以做而实际上未能做。
You could have done better, but you didn’t try your best.
cannot+ have done：表示对现在或过去行为的否定推测。
③Had I been free,I would have visited you.
混合虚拟条件句
不同时间的虚拟：各遵守各的规则
①If he had listened to me, he would not be in trouble now.
②If he had told me yesterday,I should know what to do now.
need
need作为情态动词只有一种形式，只用于否定句和疑问句。
dare
dare作为情态动词用时有两种形式：dare和dared两个词形，除了可以用于否定句和疑问句外，还可以用于条件从句或表示怀疑的句子中。
If he dare come,I will kick him out. I don’t know whether he
for I worked to use it.
注意：He should have finished the workby now.（表推测）
虚拟语气
类别
用法
例句
If引导的
条件从句
与现在事实相反
从句动词：过去式（be用were）
主句动词：should/would/could/might+do
If he were here, he would help us.
would可表示过去反复发生的动作或某种倾向。
During the vacation he would visit me every week
The wound would not heal.（伤口老是不能愈合）
would表示估计或猜想。
It would be about ten when he left home.
表示能力的情态动词用can/could
A computer_____think for itself; it must be told what to do.
A.can’tB.mustn’t C.may not D.might not
表示许可时用may/might ,can/could都可以，但在问句中用could…?或might…？以使口气委婉客气，其回答一定要用can或may，以使回答口气明确（must表示一定，必须，mustn’t表示禁止，不许可）。
I should(ought to) help him because he is in trouble.
will/would
请求、建议，would比will委婉客气。
Would you pass me the book?
表示意志、愿望和决心。
I will never do that again.
They asked us if we would do that again
③If I were you, I would have gone to her birthday party.
虚拟与陈述的混合：各遵守各的规则
①He could have passed the exam,but he wasn’t careful enough.
②You should have come earlier.The bus left a moment ago.
应当（表示义务责任，口语中多用should）
ought not to/oughtn’t to do
Ought…to do…?
Yes,…ought.
No,…oughtn’t.
shall
用于一三人称征求对方意见、二三人称许诺、命令、警告、威胁等
shall not/shan’t do
Shall…do…?
Yes,…shall.
①—Could I call you by your first name? —Yes, you______
A.will B.couldC.mayD.might
②Johnny, you_____play with the knife, you_____hurt yourself.
A.won’t/can’tB.mustn’t/may
C.shouldn’t/must D.can’t/shouldn’t
在肯定句中could不可以用来表示过去某一特定场合的能力，而要用was/were able to。
The fire spread through the hotel very quickly but
everyone_____get out.
A.needn’tB.can’tC.should D.may
在疑问句只能用can，不能用may和must。
He may be very busy now. Can he be very busy now?
He must be very busy now. Can he be very busy now?
No,…shan’t.
should
应当，应该（表义务责任）
本该（含有责备意味）
should not/shouldn’t do
Should…do…?
will
意愿，决心
请求，建议，用在问句中would比较委婉
will not/won’t do
Will/Would…do…?
Yes,…will.
No,…won’t.
should(ought to)+ have done：本来应该做而实际上又没有做。其否定形式表示某中行为不该发生却发生了。
You should have started earlier, but you didn’t.
She shouldn’t have taken away my measuring tape,
dare say.
注意:He doesn’t dare(to)answer the question.（否定句）
Does she dare(to)enter the dark room?（疑问句）
shall
用于第一人称：征求对方的意见。
What shall we do this evening?
用于第二、三人称：警告、命令、允诺、威胁等。
A.mustB.mayC.can D.will
而can表示的是逻辑上的可能性：
Mary is in poor health. She can be ill at any times.
在否定句中只能用can和may。所以can’t时用以代替mustn’t，语气比may更肯定。中文可以翻译为不可能。
Michael______be a policeman, for he’s much too short.
If we had taken the other road, we might have arrived earlier.
must+ have done：对过去发生的行为肯定的推测。
其否定式为：cannot have done。
You must have seen the film.
You cannot have seen the film.
可以（问句中表示请求）
可能，或许（表推测）
祝愿（用于倒装句中）
may not do
May…do…?
Yes,…may.
No,…mustn’t/can’t.
might
might not do
Might…do…?
Yes,…might
No,…might not.
must
必须，应该（表主观要求）
肯定，想必（肯定句中表推测）
would
would not/wouldn’t do
dare
敢（常用于否定句和疑问句中）
dare not/daren’t do
Dare…do…?
Yes,…dare.
No,…daren’t.
need
需要,必须（常用于否定句和疑问句中）
need not/needn’t do
Need…do…?
Yes,…must. No,…needn’t.
used to
过去常常（现在已不再）
used not/usedn’t/usen’t to do
didn’t use to do
Used…to do…?
Did…use to do…?
Yes,…used.
No,…use(d)n’t.
Yes,…did.
No,…didn’t.
II.情态动词的重点知识
表示“能力、许可”的can和may
含蓄虚拟
条件句
but for+名词表示虚拟条件
句子或主句中的谓语动词的形式视具体情况而定。这是考查考生应变能力的最佳试题。
---But for your timely warning,we ______
into great trouble.
---You know we’re friends.