高考英語情態動詞語法講解
1、情態動詞 + have done sth
這個結構有著特殊意義：用來表示猜測（設想可能發生過什么事情）或
想象（設想可能出現過什么不同的情況）
①should (ought to) have done sth 本來該做而未做
This wall oughtn’t to have been painted blue.
②need have done sth 本來有必要做而未做
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 對過去所做動作的否定或疑問推測
I don’t think he can have heard you. Call again.
Where can John have put the matches?
⑤may (might) have done sth 過去可能發生某事，與could相比，may和 might可能性較小，might 可能性更小；might 也可表示過去可能發生而未發生的事情。
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
●推測過去可能發生某事 （同can, 但can不用肯定句）
She could have gone off with some friends.
●表示過去沒有實現的可能性：某事可能發生，但卻沒有發生
You were stupid to go skiing there----you could have broken your leg.
●表示有能力做而未做（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 表示能力
●can 通常表示現在的或一般的能力---即你無論什么時候想做就能
做到的能力, 指單純的表示一個人有某種能力。
You can certainly cook, even if you can’t do anything else.
●be able to表示某人通過努力、克服困難做成某事。
will be able to 表示將來的能力
I’ll be able to speak German in another few months.
●could 表達 一般的能力---即你過去想干什么就可以干什么
She could sing like an angel when she was a kid.
但could 不能表達過去某種具體的能力，此時用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
●可用來表示：①理論上的可能性（不涉及是否真發生）；②提出建議
（提出解決某個問題的可能辦法或者采取的行動）；③在問句或否定句中表達現在的可能性）
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可用來表達：①將來的可能性；②說話時某事可能是真實的
We may go climbing this summer.①
You may be right.②
●could / might可用來表示：①說話時某事可能是真實的；②將來
某事有可能發生，但不表示特別可能發生。
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請求允許：它們都可以表示請求允許做某事,could 和 might并不是表示過去
Can (May, Could) I borrow your umbrella ?
②允許：當我們允許某人做某事時，我們用can和may來表達，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 有拒絕的意思）
Could I use your phone?
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