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1、GRAMMAR GUIDEModal verbs ()n ought to, have to, mustnt，neednt寻规找矩 观察下列三组句子，注意情态动词ought to， have to， mustnt和neednt的不同用法。1. ought to1) You oughtnt to make private phone calls in work time.在工作时间你不应该打私人电话。2) He ought to be there by now.他现在应该到那儿了。3) Ought I to write to apologize to her？我应该向她写信道歉吗？4) They
2、 ought to come tomorrow, oughtnt they (= shouldnt they)? 他们应该明天来，是吗？2. have to1) My brother was very ill, so I had to call the doctor in the middle of the night. 我弟弟病得很厉害，我只得半夜里把医生请来。2) Must I finish the task right now？我现在必须完成这项任务吗？Yes, you must. / Yes, you have to. 是的，你必须。（No, you neednt. / No, you
3、 dont have to. 不，不必。）3) You dont have to tell him about it.你不必把此事告诉他。4) Do you have to go now. 你现在就得去吗？Yes, I do. 是的，我必须去。3. mustnt与neednt1) Smoking must not be allowed in the office.严禁在办公室吸烟。2) Must we hand in our exercises today?我们今天必须交作业吗？Yes, you must. 是的，必须交。（No, you neednt (you dont have to).不
4、，不必今天交。）3) It must be that naughty boy crying outside.肯定是那个调皮的孩子在外面大叫。It cant be him, because he has gone to school.不可能是他，因为他已经去上学了。4) There are still one and a half hours to go. We neednt be in such a hurry. 还有一个半小时，我们不必如此慌慌张张。归纳总结通过观察分析以上几组例句，我们可以对ought to, have to, mustnt和neednt的用法归纳如下：1. ought t
5、o 意为“应当；应该”，一般可与should互换，但ought to语气更强，且多与责任、义务相关。如例1、4。 否定式是ought not to或oughtnt to。如例1； 可以表示猜测。如例2； 疑问式是将ought提前。如例3； 在变为反意疑问句时，疑问部分用ought或should。如例4。2. have to 表示一种客观的需要，意思是“不得不”。 如例1； 有人称、数和时态的变化。如例1; 否定形式是dont / doesnt / didnt have to，相当于neednt。如例2、3; 疑问式是在其前面用助动词do / does / did。如例4。3. mustnt 与
6、neednt mustnt表示禁止。如例1； 用must提问时的否定回答须用neednt / dont have to。如例2； mustnt与dont have to的意思大不相同，前者表示“禁止”，意思是“一定不能”；后者表示“没有必要”，意思是“不必”，相当于neednt。如例2； must常用于肯定句中表示猜测、推测，意为“一定”；表示“不可能”时要用cant。如例3； need用于否定句和疑问句中意为“必要”。如例4。学以致用用以上情态动词的适当形式填空。1. One cross the street against the red light.2. His mother is ill, so he take care of her.3. I have to stay at home preparing my lessons.But you . Tomorrow is Sunday.4. Mikes father is ill, but you tell him, because he is to take an important examination.Key: 1. ought not to / mustnt2. has to3. neednt / dont have to4. mustnt