高一英語必修3第2單元導(dǎo)學(xué)案情態(tài)動詞（II）
導(dǎo)學(xué)案4情態(tài)動詞（ii）
一、ought to 應(yīng)該，應(yīng)當 其否定 “ought not to” 或 “oughtn’t to”
(1) 用于第一人稱，表有責(zé)任或有必要做某事。
we ought to be more careful with our homework.
(2) 用于二、三人稱，表建議或勸告。
you ought to follow your teacher’s advice.
she ought not to go alone.
(3) ought to+have done: 本該……
i’m sorry. i ought to have told you this morning.對不起，我本該今天早上告訴你的。
二、have to / don’t have to / mustn’t
(1) have to = have got to 必須，不得不 （有人稱和數(shù)、時態(tài)的變化）
he has to work on the farm all day . 他不得不在農(nóng)場工作一整天。
（2）don’t have to 不必……
you don’t have to buy a computer.
(3) mustn’t 禁止，不許
you mustn’t sleep in class!
三、need 需要，必要（既可以作情態(tài)動詞，也可以作實義動詞，但用法不同）
（1）作為情態(tài)動詞，need 通常用于否定句和疑問句
①you needn’t buy the book..
②——need he do his homework first?
——yes ,he must! (no ,he needn’t)
(2) need 作為實義動詞時，通常用法是：
sb/sth need to do (表主動) we need to tell him the truth.
sb/sth need doing /to be done（表被動） my car needs repairing./my car needs to be repaird
sb need sth 某人需要…… mary needs your help.
三、情態(tài)動詞+have done
1. must have done 推測過去“肯定……”
he must have played computer games last night.
2 may / might have done 推測過去“也許……”
he might have known the answer to the question.
3.(1)could have done 用于疑問句時，表示 推測過去“可能……？”
could he have finished the task? 他可能把任務(wù)完成了嗎？
（2）could have done 用于肯定句時， 表“能夠做而沒有做”
i could have finished the work on my own. 我本能夠獨自完成工作.
4. (1)should have done 本應(yīng)該做而沒有做
you should have studied hard.
(2) shouldn’t have done 本不該做而做了
you shouldn’t have told lies.
5. ought to have done: 本該做而沒做
6. needn’t have done 本不必…… 本沒必要……
you needn’t have told me the news.