如题所述
一、《新概念英语》中的must
在《新概念英语》经典版中，must出现的频率较高，分别出现在第一册第43-46课、第61-66课、第77-80课、第125-132课以及第二册第17课、第41课、第65课、第89课。
must比较常见的用法是：表义务或要求等的“必须”;表猜测的“肯定，一定”。
二、表义务或要求等
这时，must表示“必须”。如：
肯定句：He must have some water after the heavy work.
否定句：He needn't have any water after the heavy work.
一般疑问句及其回答：Must he have any water after the heavy work? Yes, he must. / No, he needn't.
划线部分提问：What must he do after the heavy work?(假如划线部分为have some water的话)
【注意】
(一)mustn't与needn't
很多学生一说到must的否定，首先想到的一般都是mustn't。所以，老师需要提醒学生注意：must表必须时的否定形式是needn't(不必)，而不是mustn't(禁止，不能)。
(二)must与have to
虽然have to(不得不，必须)经常被归到情态动词里，但其实have to并不是情态动词，这里的have其实是实义动词，从句子功能来讲，就跟work或play等动词的基本用法是一样的。它与must的区别主要有：
1、must没有时态、人称和数的变化，而have to有时态、人称和数的变化。如：
must：She must go home right away.
have to：She has to go home right away.
再比如：
must：She must attend the meeting yesterday.
have to：She had to attend the meeting yesterday.
2、因为must没有时态的变化，而have to有，所以在句型转换中，要注意两者的区别。如：
1)must
肯定句：She must attend the meeting yesterday.
否定句：She needn't attend the meeting yesterday.
一般疑问句及其回答：Must she attend the meeting yesterday? Yes, she must. / No, she needn't.
划线部分提问：What must she do yesterday? (假如划线部分为attend the meeting的话)
2)have to
肯定句：She had to attend the meeting yesterday.
否定句：She didn't have to attend the meeting yesterday.
一般疑问句及其回答：Did she have to attend the meeting yesterday? Yes, she did. / No, she didn't.
划线部分提问：What did she have to do yesterday? (假如划线部分为attend the meeting的话)
3、must多表示主观需要或责任感的驱使，认为有必要或有义务去做某事，一般译为“必须”，而have to多表示客观存在的环境所限，即客观要求而无奈为之，一般译为“不得不做某事”。如：
主观认为、无人*：I must clean the kitchen because it is too dirty. (因为太脏了，我必须要打扫房间。)
客观所逼、不得不做：I have to do my homework now.(我现在不得不做作业。)
4、尽管have to与must存在以上区别，在must的否定句以及一般疑问句的否定回答中，也经常可以用have to来替换needn't。如：
肯定句：She must attend the meeting yesterday.
否定句：She needn't/doesn't have to attend the meeting yesterday.
一般疑问句及其回答：Must she attend the meeting yesterday? Yes, she must. / No, she needn't/doesn't have to.
三、表猜测
我们在“情态动词can的考点用法”一文中，已经提到，can't表达的是否定猜测，而must则表示肯定猜测，意思是某人或某物一定或肯定会怎么样。
与can't一样，must主要用来表示对现在时间或是过去时间发生的事情的肯定猜测。
(一)对现在时间的猜测
此时，must可以用来表示对现在的状态或动作进行猜测。如果是状态，must后面直接跟表状态的谓语动词即可;如果是动作，must后面的谓语动词则要采用be doing的形式。如：
状态：He must be over 40 years old. (他肯定有四十多岁了。)
动作：He must be reading in the library now. (他现在肯定正在图书馆看书。)
(二)对过去时间的猜测
此时，must后面的谓语动词如果是状态，则采用“must have+表状态的动词的过去分词”;如果是动作，则采用“must have done”的形式;如果是过去进行的动作，则采用“must have been doing”的形式。如：
状态：He must have been in the bathroom when I called him last night.
动作：He must have finished his homework before dinner yesterday.
过去进行：He must have been listening to loud music, for he didn't answer my call.
四、特殊用法
(一)表偏偏
此时，must表达的是说话者不耐烦的语气或是与说话者愿望相反的情况。如：
Why must you come in at this moment? (你为什么偏偏在这个时候进来?)
(二)用作名词
must也可以直接用作普通名词，表示“必须做的事，必需的东西”。如：
A raincoat is a must in the rainy season. (在雨季雨衣是必备之物。)
His new novel is a must for all lovers
