情态动词must的用法

吴怀霞

must的用法比较多,而且难掌握,现归纳如下;

1. must的意义

(1)表示责任,义务, 意为“必须”。如:

You must tell me the truth.

(2)强调语气的肯定,意为“一定要”。如:

I must ask you about your family.

(3)表示推测,意为“想必”。如:

He must be at home; the light is on.

2. must 的时态

must只有一种形式, 在将来时里,可用must, 也可用 shall(will) have to。如:

I must be at home tomorrow.

I shall have to go there some day.

must 一般不用于过去时态,它的过去式常用had to代替。如:

I had to go there yesterday.

但在下列情况下must也可用过去时:

(1)在间接引语中。如:

He said that he must talk with his teacher.

He decided that he must try to be on the side of the winner.

I said you mustnt go there.

(2)作推测解时。如:

He must have gone to Beijing yesterday.

(3)作“偏偏”解时。如:

Just when they were about to go there, they must catch a bad cold.

3. must的否定式及其答语

(1)当must意为“必须”时否定式是neednt。如:

You must pay the money, but you neednt do so at once.

Must I finish my homework now?

Yes, you must./No, you neednt.

其否定也可用dont have to。如:

You must be back by 12 oclock. 变为否定句应是:

You neednt be back by 12 oclock. 或 You dont have to be back by 12 oclock.

(2)当要表达“绝对不可,不许”时,其否定式是mustnt。如:

You mustnt do that.

You mustnt smoke, must you?

I mustnt let anyone know.

I must save money, mustnt I?

(3)表示“推测”时 其否定式为cant。如:

He must be there.

He cant be there.

(4)——May I come in?

——No, you mustnt.

4. must 与 have to

一般情况下可以通用。如:

You must(have to) do as you are told.

但:(1)表示主观上认为的责任或义务时用must。如:

We must try our best to do it.

(2)表示命令时用must。如:

You must answer my question in English.

(3)表示客观条件不得不如此时,用 have to。如:

He missed the bus and had to walk home.

(4)must的否定式表示“绝对不可,不许, 禁止”,have to的否定式表示“不必”。如:

You mustnt smoke in class.

You dont have to go there.