Obligation: Must and Have To helps you communicate about internal and external obligation, prohibition and no necessity. Start with the meaning, notice the pattern, and then use it in complete sentences.
By the end of this lesson, you can
- I can express rules, necessity and lack of necessity using must and have to.
- Recognise and build the form: must + base; have/has to + base; don't have to; mustn't.
- Use the pattern accurately in a meaningful sentence.
Meaning and use
Use Obligation: Must and Have To for internal and external obligation, prohibition and no necessity. Always read the whole situation before choosing the form: grammar expresses a meaning, not only a pattern.
You must wear a seat belt in a car.
Use 'must' to express a strong rule or obligation.
I have to start work at seven because of company policy.
Use 'have to' for an obligation imposed by an external rule.
She has to take the early train tomorrow.
Use 'has to' with a third-person singular subject.
must + base; have/has to + base; don't have to; mustn'tKeep this pattern visible while you study the examples. Then cover it and rebuild one example from memory.
Key rules to notice
These rules explain why the form is correct. Focus on the subject, auxiliary, verb form, word order and time or meaning clues.
- Use 'must' to express a strong rule or obligation.
- Use 'have to' for an obligation imposed by an external rule.
- Use 'has to' with a third-person singular subject.
- 'Mustn't' expresses prohibition, not lack of necessity.
- 'Don't have to' means there is no necessity.
Common mistakes
Not:You might wear a seat belt in a car.
Use:You must wear a seat belt in a car.
Use 'must' to express a strong rule or obligation.
Not:I must to start work at seven because of company policy.
Use:I have to start work at seven because of company policy.
Use 'have to' for an obligation imposed by an external rule.
Not:She have to take the early train tomorrow.
Use:She has to take the early train tomorrow.
Use 'has to' with a third-person singular subject.
Check before you practise
Complete each sentence mentally, then reveal the answer.
You ____ touch the equipment without permission.
mustn't
'Mustn't' expresses prohibition, not lack of necessity.
We ____ bring food; lunch is provided.
don't have to
'Don't have to' means there is no necessity.
____ you have to work last weekend?
Did
Use 'Did ... have to' for a past obligation question.