FluencyLab
GrammarHub
Distinguish necessity, lack of necessity and prohibition using have to and must forms.
Overview
Distinguish necessity, lack of necessity and prohibition using have to and must forms.
Form and rules
Use have to for rules or practical necessity: I have to wear an ID card.
Use must for strong personal obligation or strong rules, especially in notices and instructions.
Don't have to means there is no necessity; the action is optional.
Mustn't means prohibition: the action is not allowed.
Use had to for past necessity; must has no normal past form for obligation.
A closer look
Mustn't means prohibition: the action is not allowed.
Use had to for past necessity; must has no normal past form for obligation.
Examples
I have to start work at eight.
You must wear a seat belt.
You don't have to come early.
You mustn't smoke here.
We had to cancel the meeting.
Common mistakes
The rule creates a necessity, so have to fits.
Mustn't expresses prohibition.
Ready to practise?
The test combines multiple choice, gap completion, error correction, and sentence building so students have to recognise and produce the grammar, not simply reread the rule.