Learn Must and Mustn't: Expressing Rules and Importance (A1 English Grammar) — A1 English grammar lesson by Langcom

Learn Must and Mustn’t: Expressing Rules and Importance (A1 English Grammar)

劳尔-马吉尼亚

Langcom 创始人 | 剑桥考试和SIELE考试考官

9 月 24, 2026

A1✏️ 语法⏱️ 阅读时间 3 分钟📅 更新于 2026 年 9 月
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我们使用 must to talk about things that are very important or necessary to do. It’s like saying ‘you have to do this’ or ‘it is a rule’. For example, You must listen to your teacher. This means it is a very important rule, and you have no choice. We also use must for strong advice or when we are sure about something. For things that are not allowed or are forbidden, we use mustn’t (which is short for must not). It means ‘you cannot do this’ or ‘it is against the rules’. For instance, You mustn’t touch the fire. This is a rule that says touching fire is dangerous and not allowed. Remember, mustmustn’t are modal verbs. They do not change form for different subjects (like I must, he must, they must), and we always use the base form of the main verb after them.

What is ‘must’ for?

我们使用 must to talk about things that are very important. It shows a strong obligation or a rule.

  • Obligation or Necessity: When something is necessary to do. For example, Students must wear a uniform.
  • Strong Advice: When you think something is a very good idea. For example, You must visit the museum; it’s amazing!

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What is 'mustn't' for?

我们使用 mustn't (或 must not) to talk about things that are not allowed. It shows a prohibition.

  • Prohibition: When something is forbidden or against the rules. For example, You mustn't take photos in the museum.
  • Danger: When something is dangerous to do. For example, Children mustn't play with knives.

How do we form sentences with 'must' and 'mustn't'?

Mustmustn't are easy to use! They are modal verbs, so they follow simple rules.

  • Always use the base form of the verb: After mustmustn't, the next verb is always in its basic form (e.g., go, eat, study).
  • No 'to': We do not use to 之后 mustmustn't.
  • No '-s' for 'he/she/it': Must never changes its form, even for he, she, 或 it.
Forms of <span data-no-translation>Must</span> 和 <span data-no-translation>Mustn't</span>
主题 肯定式 否定形式
I / You / We / They must go mustn't go
He / She / It must go mustn't go

示例

  • I must finish my homework before dinner.
  • You must be quiet in the library.
  • He must wear a helmet when he rides his bike.
  • We mustn't talk during the exam.
  • She mustn't forget her passport for the trip.
  • They must arrive on time for the meeting.

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西班牙语母语者常犯的错误

Many Spanish speakers make small mistakes with mustmustn't. Here are the most common ones to avoid:

  • Using 'to' after mustmustn't:
    • You must to study.
    • You must study.
  • Adding '-s' to must for 'he', 'she', 'it':
    • He musts go.
    • He must go.

常见问题

What is the main use of 'must'?

Must is for strong rules, obligations, or things that are very important to do. For example, You must listen to your parents.

What is the main use of 'mustn't'?

Mustn't is for things that are not allowed or forbidden. For example, You mustn't run in the corridors.

Can I say 'must not' instead of 'mustn't'?

是的,, must not 是全称,而 mustn't is the short, common form. They mean the same thing.

Does 'must' change for 'he/she/it'?

不,, must never changes its form. It is always must for all subjects (I, you, he, she, it, we, they).

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关于作者:劳尔·马吉尼亚

劳尔·马吉尼亚是Langcom教育协会的主任,该协会是位于 您的国家. 凭借在语言教育和国际认证领域十余年的经验,他已帮助来自25个国家的数千名学生、教师和教育机构考取了剑桥英语证书以及IELTS、TOEFL和Michigan英语证书。.

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