情態動詞must的用法

吳懷霞

must的用法比較多,而且難掌握,現歸納如下;

1. must的意義

(1)表示責任,義務, 意為“必須”。如:

You must tell me the truth.

(2)強調語氣的肯定,意為“一定要”。如:

I must ask you about your family.

(3)表示推測,意為“想必”。如:

He must be at home; the light is on.

2. must 的時態

must只有一種形式, 在將來時里,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 一般不用于過去時態,它的過去式常用had to代替。如:

I had to go there yesterday.

但在下列情況下must也可用過去時:

(1)在間接引語中。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)作推測解時。如:

He must have gone to Beijing yesterday.

(3)作“偏偏”解時。如:

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

3. must的否定式及其答語

(1)當must意為“必須”時否定式是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. 變為否定句應是:

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

(2)當要表達“絕對不可,不許”時,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“推測”時 其否定式為cant。如:

He must be there.

He cant be there.

(4)——May I come in?

——No, you mustnt.

4. must 與 have to

一般情況下可以通用。如:

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

但:(1)表示主觀上認為的責任或義務時用must。如:

We must try our best to do it.

(2)表示命令時用must。如:

You must answer my question in English.

(3)表示客觀條件不得不如此時,用 have to。如:

He missed the bus and had to walk home.

(4)must的否定式表示“絕對不可,不許, 禁止”,have to的否定式表示“不必”。如:

You mustnt smoke in class.

You dont have to go there.