解读“have to”与“must”的用法

王玉萍

have to意為“必须;不得不”

强调外界客观因素要求主语“不得不做某事”，表示客观上的需要，有人称和时态的变化，其后接动词原形。have to可用于多种时态，形式随时态变化而变化，还可以用在其他情态动词之后。具体用法如下：

1. have to后接动词原形，意为“必须做……;不得不做……”。如：

We have no food home， you have to go and get some， Tom. 家里没有食物了，汤姆你得去买一些来。

2. have to 有人称、数和时态的变化，其第三人称单数形式为has to，过去式形式为had to。如：

She has to help her mom make dinner. 她不得不帮她妈妈做晚饭。

I had to do my homework last night. 我昨晚必须做作业。

3. 含有have to， has to的句子需分别借助动词do， does构成疑问句或否定句。如：

Do they have to go now？ 他们必须现在回家吗？

You don't have to go if you don't want to. 如果你不想去，你就不必去。

must意为“应该，必须”，mustn't意为“不应该，不准，不允许，禁止”。

使用must应注意以下几点：

1. must表示主观义务，意思是“应该，必须，一定”，其否定式mustn't意为“不应该，不准，不允许，禁止”。而不表示“不必”。如：

We must get there before five o'clock. 我们必须在五点前赶到那里。

You mustn't be late for school. 你千万不要上学迟到。

对用must所提问题的否定回答，常用needn't或don't have to，意为“不必”。如：

Must I stay here after school？ 放学后我还要留在这里吗？

No， you needn't / don't have to. 不，没有必要。

—Must I clean all the rooms？ 我必须打扫所有的房间吗？

—No， you needn't / don't have to. 不，你不必。

2. must表示推测，意为“一定，必定”（用于肯定句中）。

He must be our headmaster. 他肯定是我们的校长。

【巩固训练】

I. 选择填空。

1. At school I ___ wear a uniform and I___ keep my hair short.

A. can't; have to

B. have to; must

C. don't have to; must

D. does; has to

2. —Must I return the book this week？

—No， you ___. You can ___ it for 20 days.

A. mustn't： keep   B. needn't; borrow

C. needn't; keep D. mustn't; borrow

3. —Can you please stay here a little longer？

—Sorry， I ___. I ___ eat dinner with my mother. She's coming.

A. mustn't; will have to

B. don't; have to

C. can't; had to

D. can't; have to

4. —___ does Jim ___ study hard these   days？

—He will take an exam next week.

A. How; have to    B. Why; have to

C. What; have to   D. When; has to

5. Mrs Green ___ go far if she goes shopping. The supermarket is beside her neighbourhood.

A. have to         B. doesn't have to

C. needn't have to D. haven't to

6. This book ___ Tom's， because his name    is on the book.

A. maybe         B. may be

C. must be         D. must

7. The girl in the classroom ___ be Maria. She called me from the library just now.

A. mustn't     B. may not

C. can't     D. needn't

8. We ___ use mobile phones when the plane takes off.

A. may not       B. couldn't

C. needn't       D. mustn't

9. It's raining， so I ___ stay at home.

A. have to       B. can't

C. don't have to   D. needn't

10. —How do you usually go to school？

—My school is far away. I ___ take the bus to school.

A. need   B. might

C. have to       D. may

II. 按要求完成下列句子，每空一词。

1. Zhang Lin has to clean her room on Friday.（改为否定句）

Zhang Lin ___ ___ ___ clean her room on Friday

2. Mary has to help her mother with cooking. （改为一般疑问句）

___ Mary ___ to help her mother with cooking？

3. They have to do some cleaning on Sunday. （對画线部分提问）

___ ___ they have to ___ on Sunday？

4. Children  must sit in the front seat of a car. （改为否定句）

Children ___ sit in the front seat of a car.

5. —Must I hand in （上交） my homework now， Mr. Smith？

—No， you ___. （否定回答）

III. 填入方框内单词，使句意完整通顺，使用次数不限。

have to  must  can  can't  mustn't

1. I ___ arrive late for class. I ___ be on time.

2. I ___ keep my hair short and wear a school uniform.

3. I ___ listen to my teachers carefully in class. I ___ talk with my partner.

4. I ___ be noisy in the classroom. I ___ be quiet.

5. I ___ eat in the classroom. I ___ eat in the dining hall.