Must, Have To and Should: Rules, Necessity and Advice
Compare must, have to and should for rules, necessity and advice. Learn the key difference between mustn't and don't have to with everyday practice.
Use must and have to to express necessity or obligation, and should to give advice in everyday situations. Pay special attention to the negatives: “You mustn't do it” means it is not allowed, while “You don't have to do it” means it is not necessary. That difference can change the message completely.
Compare the main meanings
Form | Everyday use in this lesson | Example |
|---|---|---|
must | A strong requirement or necessity | Visitors must sign in at reception. |
have to | A requirement or practical necessity | I have to finish this form today. |
should | Advice or a recommended action | You should check the date before sending it. |
mustn't | A prohibition | You mustn't open that door. |
don't have to | No necessity | You don't have to print the form. |
Scroll sideways to see all columns.
Must and have to overlap. Have to is common when explaining a requirement or circumstance; must can express a strong personal necessity and also appears in rules and notices. It is too simple to say must is always personal and have to is always external.
Build the positive forms
Use must or should followed by a base verb, without to: “I must leave” and “You should call”. They do not take an -s with he or she: “She must leave”, not “She musts leave”.
Have to changes like have: “I have to leave”, “She has to leave” and “We had to leave yesterday”. For a past obligation, had to is the useful form: “I had to change my appointment”.
For practical phrases around scheduling, use making and changing an appointment. For softer requests to another person, compare can, could and would.
Keep the negatives separate
Imagine a class where homework is optional. “You don't have to do the extra exercise” means you may do it, but it is not required. “You mustn't do the extra exercise” would tell learners not to do it.
Similarly, “You shouldn't interrupt” gives advice about an action, while “You mustn't interrupt” presents it as a prohibition. The best choice depends on what you mean and the situation, rather than simply which word looks more polite.
Not allowed: “You mustn't write on this copy.”
Not required: “You don't have to bring a notebook; paper is provided.”
Advice against an action: “You shouldn't leave this until the last minute.”
Ask questions with the right pattern
Use do or does with have to: “Do I have to book?” and “Does she have to attend?” Notice that have returns to its base form after does. For the past, ask “Did you have to wait?”
With should, put it before the subject: “Should I email or call?” A question such as “Do I have to come?” asks whether attendance is required. “Should I come?” asks for advice about attending.
Must can also begin a question, but “Do I have to …?” is a useful everyday choice for checking a requirement. If the answer matters, confirm the practical details as well.
Your turn · self-review
Choose the meaning
Write the sentence you need before comparing it with the model.
Practice only. Your writing stays on this page; it is not submitted or saved.
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Model answer and explanation
“You don't have to print it.” This says printing is not necessary. Mustn't would incorrectly say printing is prohibited.
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Model answer and explanation
“She must call today. Does she have to pay now?” Use the base verb after must and have after does.
Use advice with a reason
“You should review these words tomorrow because they are new to you” gives the listener a useful reason. You can also ask what they need before suggesting a solution: “Which part is difficult?” Advice works better when it connects to the actual situation.
For a different opinion about a plan, giving your opinion politely offers related phrases. If you need to explain a problem and request a next step, try making a polite complaint.
Practise a short exchange
Try: “Do I have to bring a printed ticket?” “No, you don't have to. A digital copy is fine, but you must show it at the entrance.” Change ticket to another everyday requirement and keep the negative meaning clear.
For reference, the British Council guide to permission and obligation explains related uses. These words have other meanings too; begin with the obligation and advice examples here, then notice them in context.
