B1 — IntermediateGrammar· Modal verbs
Modals of Obligation and Advice
Use must, have to, should, ought to and had better to express rules, advice and absence of obligation.
15 min Medium
Obligation
- must: the speaker's own rule - I must finish this tonight.
- have to: an external rule - You have to wear a helmet on site.
- mustn't: prohibition - You mustn't smoke here.
- don't have to: no obligation - You don't have to come if you are tired.
Advice
- should / ought to: You should rest.
- had better (+ warning): You had better leave now or you will miss the bus.
mustn't and don't have to are completely different. One forbids, the other frees you.