Must and must not — Foreign languages, 7–10
Use must and must not to say that a rule or strong need applies. Foreign languages, 7–10 years.
A rule or strong need
Must tells us that something is required: You must wear a helmet. Must not, often written mustn’t, tells us that something is forbidden: You mustn’t touch the hot pan. After must, use the plain verb: must go, must listen, must be. The verb does not change for he or she.
Why rules need a strong word
A sign saying You must wash your hands is stronger than You can wash your hands. It tells you that safety or another person’s rule requires the action. You mustn’t run near the pool gives the matching boundary. These words solve the problem of making permission, advice and obligation different.
Turn a safety rule into English
The rule is: wearing a seat belt is required in the car. Step one: choose must because it is an obligation. Step two: name the person with you: You. Step three: add the plain verb phrase: wear a seat belt. The sentence is You must wear a seat belt. For a ban, use You mustn’t stand up.
Must does not mean can
It is reasonable to confuse must and can because both are short helper verbs. But can says something is possible or allowed, while must says it is required. You can use a pencil means it is an option; You must use a pencil means there is no choice. The strength of the message changes.
Signs, games and shared spaces
You see must and mustn’t on signs, instructions and safety messages: Visitors must show a ticket; Players mustn’t move the pieces yet. They are useful when many people need the same rule quickly. Use them for real requirements, not for every small preference.
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