must,ought to 二词的区别与用法

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must,ought to 二词的区别与用法
must,ought to 二词的区别与用法

must,ought to 二词的区别与用法
1 情态动词的语法特征
1）情态动词不能表示正在发生或已经发生的事情,只表示期待或估计某事的发生.
2）情态动词除ought 和have 外,后面只能接不带to 的不定式.
3）情态动词没有人称,数的变化,即情态动词第三人称单数不加-s.
4）情态动词没有非谓语形式,即没有不定式,分词,等形式.
must表示推测
1) must用在肯定句中表示较有把握的推测,意为"一定".
2) must表对现在的状态或现在正发生的事情的推测时,must 后面通常接系动词be 的原形或行为动词的进行式.
You have worked hard all day.You must be tired.你辛苦干一整天,一定累了.（对现在情况的推测判断）
He must be working in his office.他一定在办公室工作呢.
比较：
He must be staying there.
他现在肯定呆在那里.
He must stay there.
他必须呆在那.
3) must 表示对已发生的事情的推测时,must 要接完成式.
I didn't hear the phone.I must have been asleep.我刚才没有听到电话,我想必是睡着了.
4) must表示对过去某时正发生的事情的推测,must 后面要接不定式的完成进行式.
---Why didn't you answer my phone call?
---Well,I must have been sleeping,so I didn't hear it.

must表示客观的必须，动作的发出者受条件的限制，与have to类似。
ought to与should相同表示主观的应该干……

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