Have to / Don't have to / Must / Mustn't

Have to / Don't have to / Must / Mustn't

We use have to and must when something is necessary. In positive sentences they are often the same. But the negative forms don't have to and mustn't have very different meanings, so be careful!

Structure

• Have to: Subject + have to / has to + base verb. Example: I have to work on Saturday. She has to work on Sunday.
• Must: Subject + must + base verb (the same for all subjects, no 's'). Example: You must wear a seatbelt.
• Negative: don't have to / doesn't have to (it is not necessary) and mustn't (you are not allowed). Example: You don't have to come. and You mustn't smoke here.
• Question: Do / Does + subject + have to + base verb? Example: Does he have to wear a uniform? After does, we use have, not has.
• Past: had to / didn't have to. Example: I had to work yesterday. We didn't have to pay.

How the Grammar Works

1. Use have to when something is necessary because of a rule, a boss or a situation: I have to renew my passport.
2. Use must when you think something is necessary, or when it is a strong rule or a sign: I must call my mother today.
3. Don't have to means it is not necessary. You can choose: You don't have to pay, it's free.
4. Mustn't means you are not allowed to do it: You mustn't park here.
5. For questions, use do / does + have to: Do you have to go now?
6. Must has no past form for this meaning. For the past, use had to: I had to work yesterday. For no necessity in the past, use didn't have to: We didn't have to pay.

Common Use Cases

• Rules and laws: You must wear a helmet. Drivers have to stop at red lights.
• Personal duties: I must call my mother. I have to finish this report today.
• Saying something is not necessary: You don't have to bring anything.
• Saying something is not allowed: You mustn't touch that.

Frequent Mistakes and How to Avoid Them

• Mixing up 'don't have to' and 'mustn't'. Incorrect: You mustn't pay, it's free. Correct: You don't have to pay, it's free. Use 'mustn't' only when something is not allowed.
• Adding 's' to 'must'. Incorrect: She musts finish it. Correct: She must finish it.
• Using 'to' after 'must'. Incorrect: You must to go. Correct: You must go.
• Wrong question or wrong 'have'. Incorrect: Have you to go? and He have to go. Correct: Do you have to go? and He has to go.
• Using 'must' for the past. Incorrect: I must work yesterday. and I musted work. Correct: I had to work yesterday.

Comparison with Related Grammar

In positive sentences, must and have to are often both possible: You must wear a seatbelt. and You have to wear a seatbelt. Often, have to is used for a rule or a duty from outside, and must is used for your own opinion or a written rule. The big difference is in the negative. Don't have to means it is not necessary. Mustn't means you are not allowed. These meanings are opposite, so you cannot swap them.

Example Sentences

• We have to leave early tomorrow.
• You mustn't use your phone during the exam.
• You don't have to answer if you don't want to.
• She doesn't have to work on Sunday.
• Employees must wash their hands before work.
• Does he have to wear a uniform?
• I had to get up at five o'clock yesterday.
• We didn't have to pay for the museum.

When to Use This Rule

Use have to and must when something is necessary. Remember the key difference: don't have to means it is not necessary, and mustn't means you are not allowed. For the past, use had to.