专升本英语语法-情态动词（二）

三、must 的用法

1. 表义务，“必须”

You must talk to them about their study.

2. 在否定结构中表不许、禁止

You mustn't leave here.

3. 表坚定的建议

You must come and see us as soon as you get to Shanghai.

一到上海你就得马上来见我们。

4. 表推测，暗含有很大的可能性

He must be ill. He looks so pale.

［注意］ may 暗含的可能性较小，must 暗含的可能性较大。

5. 关于 must 的简短回答：

Must I clean the dining room at once?

--Yes, you must.

--No, you needn't.

---No, you don't have to.

四、have to 的用法

have to 虽属于情态动词，但它有人称、数的变化，它的疑问句否定句的构成也

和其他情态动词有所不同。

1. have to 表客观的需要和义务，must 表主观认识

I missed the train, so I had to take a taxi.

2. 在疑问句和否定句中，have to 多用助动词 do 构成，must 则直接提前或加 not。

Did he have to do it?

――He didn't have to do it.

3. 在否定句中，have to 表示不需要，must 表不允许。

You don't have to go there.

You mustn't go there? 你不可去那儿。

4. 虽然 must 可以用在过去时态中，但是 have to 更能直接了当的表达过去时间概念。

She must see Hubert that night.

I had to leave at six yesterday.

五、need 的用法

need 既可用作情态动词，又可用作实义动词。作情态动词时，没有数和人称的

变化，后接动词原形；作实义动词时，有数的变化和人称的变化，后接带 to 的

不定式。

1. 用于否定句，表“不必”

You needn't worry.

I don't think you need worry.

2. 用于疑问句，表“需要吗”

Need you go?

3. need 用作实义动词时，要注意始终以实义动词的标准贯彻到底

-----No, I needn't.

---Yes, I must.

判断正误：

（ ）Do you need to go there?

（ ）Do you need go there?