这个结构有着特殊意义：用来表示猜测（设想可能发生过什么事情）或
想象（设想可能出现过什么不同的情况）
、賡hould (ought to) have done sth? 本来该做而未做
This wall oughtn’t to have been painted blue.
、趎eed have done sth?? 本来有必要做而未做
You needn’t have told her the news.
、踡ust have done sth?? 对过去所做动作的肯定推测
---We went to Paris.
---That must have been nice.
、躢an have done sth??? 对过去所做动作的否定或疑问推测
I don’t think he can have heard you. Call again.
Where can John have put the matches?
、輒ay (might) have done sth 过去可能发生某事，与could相比，may和 might可能性较。琺ight 可能性更。籱ight 也可表示过去可能发生而未发生的事情。
Polly’s very late----she may (might) have missed her etrain.
You were stupid to try climbing there. You might have killed youself
、辌ould have done sth ?
推测过去”可能“发生某事 （同can, 但can不用肯定句）
She could have gone off with some friends.
表示过去没有实现的可能性：某事可能发生，但却没有发生
You were stupid to go skiing there----you could have broken your leg.
表示有能力做而未做（虚拟语气）
You could have helped me !
(You were able to help me, but you didn’t.)
2、can???? could???? be able to?????? 表示”能力“
can 通常表示现在的或”一般的能力“---即你无论什么时候想做就能
做到的能力, 指单纯的表示一个人有某种能力。
You can certainly cook, even if you can’t do anything else.
be able to表示某人通过努力、克服困难做成某事。
will be able to 表示将来的能力
I’ll be able to speak German in another few months.
could 表达? ”一般的能力“---即你过去想干什么就可以干什么
She could sing like an angel when she was a kid.
但could 不能表达过去某种具体的能力，此时用was able to,? managed to 或 succeeded in 等
How many eggs were you able to get ?
3、can, could, may和might 表示”可能性“
可用来表示：①理论上的可能性（不涉及是否真发生）；②提出建议
。ㄌ岢鼋饩瞿掣鑫侍獾目赡馨旆ɑ蛘卟扇〉男卸虎墼谖示浠蚍穸ň渲斜泶锵衷诘目赡苄裕
Anybody who wants to can become a prison visitor.
、---What shall we do ?
---We can try asking Lucy for help.、
Who can that be at the door ? Can it be Polly? 、
may 可用来表达：①将来的可能性；②说话时某事可能是真实的
We may go climbing this summer. 、
You may be right. 、
could / might 可用来表示：、偎祷笆蹦呈驴赡苁钦媸档模虎诮
某事有可能发生，但不表示特别可能发生。
You could be right, but I don’t think you are. 、佟
It could rain later on this evening. 、
4、can,? could,? may 和might表示“允许”
、偾肭笤市：它们都可以表示请求允许做某事,could 和 might并不是表示过去
Can (May, Could) I borrow your umbrella ?
、谠市：当我们允许某人做某事时，我们用can和may来表达，而不能使用could和might
You may / can watch TV for as long as you like. (不用could, might; mustn’t 有“拒绝”的意思）
---Could I use your phone?? ?
---Yes, of course you can /may.? (No, you can’t / may not.)
??????? 5、can和could表示提议和请求
它们常用来提议为某人做某事或请求别人做某事，could更客气，更
含尊敬的成分，这种用法常见于陈述句和疑问句中
、偬嵋：
Can? I carry your bag ?
I could / can do the shopping for you, if you’re tired.
、谇肭蠛兔：
Could / Can you help me with this letter?
You can / could start by cleaning the car.
6、情态动词will
、僭げ馕蠢矗ǖ谝蝗顺朴胹hall)，或发布命令
---There’s someone coming up the stairs.
---That’ll be Mary.
You’ll start work at six o’clock.
、谧栽赣胍庀
I will (不用 I shall) 表示自愿做某事，或主动提出做某事，或表达坚定的意图
---Can somebody help me ?
--- I will.
I’ll break your neck.
will you常用来提出要求或下命令，或提出请求
Will? you come this way, please?
Will you have some more wine ?
用won’t表示拒绝
No, I won’t !
She won’t open the door.
7、shall
用于第一人称，表示征求对方的意见(说话人做某事)。
用于第一、第三人称疑问句中，表示说话人征求对方的意见或向对方请示。
用于第二、第三人称，表示说话人给对方的命令、警告、允诺或威胁。
8、常用情态动词的回答
、---Must we hand in our plan ?
---Yes, you must.????? (No, you needn’t.)
、---Need I come ?
---Yes, you must.????? (No, you needn’t.)
、---May I smoke here ?
---Yes, please.??? (Certainly. / Yes, you may. )
(No, you mustn’t. / may not. / Please don’t.)
、---Could / Can I offer you some coffee ??? (提议)
(---Will / Would you have some coffee ?)
---Yes, please. / Yes, I’d like some ,please. (不用Yes, you can.)
(No, thank you.)?? (不用No, you can’t.)
、---Could / Can / Would / Will? you (please) open the door ?(请求)
---Yes, of course (I will).? (No, I’m afraid I can’t.)
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