# 第一册 Lesson 126 Have to and must 不得不和必须

## 一、课文原文

本课为语法练习课，配合Lesson 125的have to和must内容进行句型操练。

**句型练习：**

1. I must leave now. → I **have to** leave now.
2. I must leave early tomorrow. → I **shall have to** leave early tomorrow.
3. I must leave yesterday. → I **had to** leave yesterday.
4. We must go there last week. → We **had to** go there last week.
5. She must wait for him tomorrow. → She **will have to** wait for him tomorrow.
6. He must answer the letter last night. → He **had to** answer the letter last night.

## 二、重点词汇详解

| 单词 | 音标 | 词性 | 释义 | 用法说明 |
|------|------|------|------|----------|
| leave | /liːv/ | v. | 离开 | leave for 出发去；leave sth somewhere 把某物留在某处 |
| early | /ˈɜːli/ | adv./adj. | 早的 | early in the morning 清早；反义词late |
| wait | /weɪt/ | v. | 等待 | wait for sb 等某人；wait to do sth 等着做某事 |
| answer | /ˈɑːnsə/ | v. | 回答 | answer the letter 回信；answer the phone 接电话 |

## 三、语法知识点

### have to 的时态变化

must只有现在时形式，要表达其他时态的"必须"，需用have to的相应形式：

| 时态 | 形式 | 例句 |
|------|------|------|
| 一般现在时 | have to / has to | I have to go now. / She has to go now. |
| 一般过去时 | had to | I had to go yesterday. |
| 一般将来时 | will/shall have to | I will have to go tomorrow. |
| 现在完成时 | have/has had to | I have had to stay here. |

### must 与 have to 的否定对比

| 否定形式 | 含义 | 例句 |
|----------|------|------|
| mustn't | 禁止，不准 | You mustn't smoke here.（你不准在此吸烟。） |
| don't have to | 不必，不需要 | You don't have to smoke here.（你不必在此吸烟。） |
| needn't | 不必（=don't have to） | You needn't smoke here. |

### must 的两种主要用法

| 用法 | 含义 | 例句 |
|------|------|------|
| 表义务 | 必须，应该 | I must water the garden. |
| 表推测 | 一定，必定 | You must be tired. |

## 四、重点句型分析

1. **I have to leave now.**（=I must leave now.）
   - 现在时have to与must可互换
   - have to更强调客观需要

2. **I shall have to leave early tomorrow.**
   - 将来时用shall/will have to
   - must没有将来式

3. **I had to leave yesterday.**
   - 过去时用had to
   - must没有过去式

4. **You mustn't tell anyone.**（你绝不能告诉任何人。）
   - mustn't表示禁止
   - 与don't have to（不必）含义完全不同

5. **You don't have to tell anyone.**（你不必告诉任何人。）
   - don't have to表示不必
   - = You needn't tell anyone.

## 五、课文翻译

1. 我现在必须离开。 → 我现在不得不离开。
2. 我明天必须早点离开。 → 我明天将不得不早点离开。
3. 我昨天必须离开。 → 我昨天不得不离开。
4. 我们上周必须去那里。 → 我们上周不得不去那里。
5. 她明天必须等他。 → 她明天将不得不等他。
6. 他昨晚必须回信。 → 他昨晚不得不回信。

## 六、语言点精讲

1. **must与have to互换**：在现在时中，表示"必须"时两者可以互换，但侧重点不同。must侧重主观看法（我认为必须），have to侧重客观需要（情况使得我必须）。

2. **must的时态限制**：must只有一种形式，用于现在时和将来时（不太正式）。表达过去必须用had to，表达将来必须用will/shall have to。

3. **mustn't与don't have to的致命区别**：mustn't表示"禁止"（强烈不允许），don't have to表示"不必"（没有义务但不禁止）。这是考试常见考点。

4. **needn't的用法**：needn't = don't have to，都表示"不必"。但need作为实义动词时用don't need to。

## 七、课后练习要点

1. 将must改为have to的各种时态形式
2. mustn't与don't have to/needn't的选择填空
3. 翻译练习：区分"禁止"和"不必"
4. 用had to改写含must的过去时句子

## 八、本课小结

- **核心语法**：have to的时态变化（have to / had to / will have to）
- **关键规则**：must无过去式和将来式，用had to和will have to代替
- **重点区别**：mustn't（禁止）vs. don't have to/needn't（不必）
- **易错点**：过去时必须用had to，不能用must