What you'll learn
By the end of this lesson, you'll be able to express strong obligation and rules with must and have to, and clearly separate prohibition (mustn't) from absence of obligation (don't have to).
When do I use it?
must and have to both express obligation. must sounds stronger and more personal — the speaker believes it is necessary. have to is more neutral and usually talks about external rules or facts.
- You must wear a seatbelt. (The speaker is insisting)
- You have to show your ID at the door. (It is the rule)
mustn't means it is forbidden. don't have to means it is not necessary — you may choose. These two are very different.
- You mustn't smoke here. (It is not allowed)
- You don't have to tip. (It is not required, but you can)
How do I form it?
must + base verb and have to + base verb. After he/she/it, use has to. Negatives are mustn't + base verb and don't/doesn't have to + base verb. Remember: no "to" after "must".
- Subject + must + base verb. You must stop.
- Subject + have to + base verb. I have to study.
- Subject + mustn't + base verb. You mustn't run.
Questions use do/does + subject + have to: Do I have to pay now?
Common mistakes for Spanish speakers
Two classic errors. First, adding "to" after "must" by mirroring "tener que": "I must to go" is wrong, it is "I must go". Second, confusing mustn't with don't have to: Spanish "no tener que" sounds like "must not", but "You don't have to come" means it is optional, while "You mustn't come" means it is forbidden. Also remember that he/she/it takes "has to", not "have to".
Opposites that pair up: must ↔ mustn't (both are strict), and have to ↔ don't have to (the negative is relaxed). "Must not" and "don't have to" are not the same.
Practice
Multiple Choice
A2Which sentence means smoking is not allowed here?
Fill in the Blank
A2She to finish the report before Friday.
Hint: With he/she/it, use 'has to'.
Find the Error
A2Practice Speaking
Apply what you've learned in a real conversation with AI feedback.
Level: A2