必修三unit2语法讲解情态动词用法.doc

必修三unit2语法讲解情态动词用法（二）

一、ought to的用法
1．ought to“应该”。与should相比较ought to语气重，偏重“责任、义务、道德、法律”等方面，意为“应该”。
①We ought to stop polluting nature. 我们应该停止污染大自然。
2．ought to 表示较大的可能性。
②Mary ought to be here soon. 玛丽应该很快就来了。
[点津]　用ought to表示推断时，语气较肯定，通常指的是一种合乎逻辑的可能性(与should表推断时相似)，有时可译为“很可能；准是”(语气比must要弱)。
3．ought to的否定形式为ought not to 或oughtn't to, 其一般疑问句形式是将ought置于主语前。
③We ought not to start so late. 我们不该这么晚动身。
4．在反意疑问句中，常省掉to用oughtn't或shouldn't。
④He ought to take back what he has said, oughtn't/shouldn't he?
他应该收回他说的话，是吗？
1－1.写出下面句中黑体部分的意义
①To keep fit, we ought to learn more about our body._______
②You ought not to do such a thing._______
③It ought to be a close game._________
1－2.用ought完成句子
④你不该责备他。You ____________(scold )him.
⑤我明天该动身吗？—______________(_leave )tomorrow?
是的，你应该。—Yes, you_ought_to．
⑥我们现在应该走，是吗？ We ought to go now, ____________?
二、have to, don't have to与mustn't的用法
1．have to(口语中常用have got to)表示客观需要做的事情，意为“必须；不得不”。有时态、人称和数的变化，其否定式和疑问式应由助动词do构成。
①My brother was very ill, so I had to call the doctor in the middle of the night.
我弟弟病了，我不得不半夜里把医生请来。
2．have to的否定式为don't have to，表示“没有义务或没有必要做某事”，意为“不必”，常可以回答must提问的一般疑问句。
②You don't have to finish the work now.
你现在没有必要完成这项工作。
[辨析比较]　
must和have to都有“必须”之意，但二者有区别：
(1)have to侧重客观需要，而must表示说话人的主观看法；
(2)have to有时态、人称和数的变化，而must只有一种形式；
(3)must的否定式mustn't 表示“禁止”。
③The magazines mustn't be taken out of the reading room.
不许把这些杂志拿出阅览室。
即学即练2
2－1.用have to完成句子
①天色太晚了，我现在得回家了。 It's too late, so I _____________ now.
②昨天我不得不离开。 I _______________ yesterday.
③他们没有必要担心核辐射。 They _____________the nuclear radiation.
④我必须马上做吗？—Must I do it at once?
不，你不必。—No, ____________．
2－2.选词填空：must, mustn't, have to
⑤现在我不得不走了，因为我妈妈生病了。
I __________ go now, for my mother is ill.
⑥我一定要戒烟。 I_______ stop smoking.
⑦晚上你一定不能独自出去。 You ________go out alone at night.
⑧(湖南高考)You ________ buy a gift, but you can if you want to.
A．must　　　B．mustn't C．have to D．don't have to
三、need的用法
1．need 作情态动词时，后跟动词原形，表示“需要；有必要”，无人称和数的变化，多用于否定句、疑问句或条件句中。
①You needn't come so early.你不必来这么早。
2．作为实义动词，同其他实义动词一样，可用于各种句式，有时态、人称、数的变化，构成否定句和疑问句时要借助于助动词do或does。
②We don't need to spend more time on it.
我们没有必要在这个事情上花太多的时间。
3－1.用need或must完成句子
①你现在不必去那儿。You needn't go there now.
②他有必要留在这儿吗？—Need he stay here?
是的，他必须。/不，他不必要。—Yes, he must．/No, he needn't．
⑤(天津高考)It's quite warm here; we ________ turn the heating on yet.
A．couldn't B．mustn't C．needn't D．wouldn't
四、情态动词＋have done的用法
1．must have done 用于肯定句，表示“过去一定做过某事”。
①How can you be late again? You must have overslept.
你怎么又迟到了？你一定是睡过头了。
2．can/could have done一般用于疑问句和否定句中，表示对过去所发生事情的推测。could have done用于肯定句时，表示“本有能力做某事而未做”。
②He can't/couldn't have watched TV last night, for he knew he would have a test. 昨天晚上他不可能看电视，因为他知道就要考试了。
③We could have arrived there before dark, but we didn't.
天黑前我们本来能够到那里的，但是没到。
3．should/ought to have done 表示“过去本应该做某事而(实际上)没有做”，含有责备或遗憾的语气；其否定形式表示某种行为不该发生却发生了。
④You should have told me earlier or I might have gone with them.
你应该早点告诉我，不然的话我就会和他们一块去了。
4．may/might have done 表示对过去发生的事情的推测，意为“也许已经做了某事，可能已经做了某事”，多用在肯定句中，用might时表示语气更加不肯定。
⑤If you had studied hard, you might have passed the exam.
如果你努力学习的话，你可能会及格的。
5．needn't have done表示“本不必做某事而实际做了”。
⑥He is old enough! You needn't have solved the problem for him.
他够大了！你根本没必要为他解决问题。
4－1.根据汉语意义，用“情态动词＋have done”填空
①你肯定看过电影《归来》。
You__________________ the film Coming Home.
②史密斯先生不可能去北京了，我刚才还在图书馆看见他。
Mr.Smith ______________ to Beijing, for I saw him in the library just now.
③本来他能够通过考试，但是他太粗心了。
He ________________the exam, but he was too careless.
④以前你应该多进行锻炼的。
You ________________more exercise before.
⑤你可能已经在报上看过这个消息。
You _______________ about it in the papers.
⑥你本不必告诉我这个消息，我已经知道了。
You _______________ me the news.I have already known it.
⑦(四川高考)—Why are your eyes so red? You _____ have slept well last night.
—Yeah, I stayed up late writing a report.
A．can't　　　　　B．mustn't C．needn't D．won't
⑧(浙江高考)I ________ myself more — it was a perfect day.
A．shouldn't have enjoyed B．needn't have enjoyed
C．wouldn't have enjoyed D．couldn't have enjoyed
⑨(陕西高考)The children ________ lost in the woods; otherwise, they would have been at the lakeside camp as scheduled.
A．must have got B．must get C．should have got D．should get
⑩(江西高考)We ____ have bought so much food now that Suzie won't be with us for dinner.
A．may not B．needn't C．can't D．mustn't

Ⅰ.选词填空
1．You _________go there alone; it's too dangerous. (mustn't/needn't)
2．It's so near; we __________ have taken a taxi.(shouldn't/can't)
3．You __________ have spent so much time playing com­puter games.(mustn't/oughtn't to)
4．—Shall I leave the room so that you two can talk?
—No, you _________. (mustn't/needn't)
5．He _______ have missed the train; he arrived at the train station two hours early.(can't/mustn't)
6．We'll be very glad if you __________join us in going camping.(can/may)
7．They____stay in the office last night because of the snowstorm.(have to/must)
8．We ________ have helped him; in that case, he would have been able to finish the work.(should/can)
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