情態動詞 have done sth

1、情態動詞 have done sth
這種結構具有特殊意義：用來表示猜測（假設可能發生了什么）或
想象(想象可能發生了什么不同的情況)
①should (ought to) have done sth  本該做卻沒有做
This wall oughtn’t to have been painted blue.
②need have done sth   本來有必要做而不做
You needn’t have told her the news.
③must have done sth   對過去所做動作的肯定推測
---We went to Paris.
---That must have been nice.
④can have done sth    對過去行動的否定或懷疑進行推測
I don’t think he can have heard you. Call again.
Where can John have put the matches?
⑤may (might) have done sth 與could相比，過去可能會發生一些事情，may和 might可能性小，might 可能性較小；might 也可以表示過去可能發生但沒有發生的事情。
Polly’s very late----she may (might) have missed her etrain.
You were stupid to try climbing there. You might have killed youself
⑥could have done sth  
“推測過去”可能“發生了什么” （同can, 但是can不需要肯定句)
She could have gone off with some friends.
這意味著過去沒有實現的可能性：事情可能會發生，但沒有發生
You were stupid to go skiing there----you could have broken your leg.
表示有能力做而不做(虛擬語氣)
You could have helped me !
(You were able to help me, but you didn’t.)
2、can     could     be able to       “表達”能力
can 通常表示當前或“一般能力”——也就是說，無論你什么時候想做，你都可以
做到的能力， 簡單地說明一個人有一定的能力。
You can certainly cook, even if you can’t do anything else.
be able to這意味著有人通過努力克服困難做某事。
will be able to 展示未來的能力
I’ll be able to speak German in another few months.
could 表達  “一般能力”——也就是說，你過去想做什么就能做什么
She could sing like an angel when she was a kid.
但could 在這個時候，它不能表達過去的特定能力was able to,  managed to 或 succeeded in 等
How many eggs were you able to get ?
3、can, could, may和might “表達”的可能性
可用表示：①理論上的可能性(不涉及是否真的發生)；②提出建議
(提出可能的解決某個問題的方法或行動)；③在問句或否定句中表達當前的可能性)
Anybody who wants to can become a prison visitor.
①---What shall we do ?
---We can try asking Lucy for help.　②
Who can that be at the door ? Can it be Polly?③
may　可用于表達：①未來的可能性；②說話的時候，有些事情可能是真的
We may go climbing this summer.　①
You may be right.②
could / might　可用表示：　①說話時有些事情可能是真的；②將來
有可能發生一些事情，但這并不意味著它特別可能發生。
You could be right, but I don’t think you are.①　
It could rain later on this evening.　②
4、can,  could,  may 和might表示“允許”
①要求允許：他們都可以表示要求允許做某事，could 和 might不代表過去
Can (May, Could) I borrow your umbrella ?
②允許:當我們允許某人做某事時，我們使用can和may不能用could和might
You may / can watch TV for as long as you like. (不用could, might; mustn’t 意思是“拒絕”)
---Could I use your phone?   
---Yes, of course you can /may.  (No, you can’t / may not.)
        5、can并向could提出建議和請求
它們通常被用來提議為某人做某事或請求他人做某事，could更客氣，更
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Tags：英語   高考