FluencyLab
GrammarHub
Distinguish external necessity, strong obligation, prohibition and advice using have to, must and should.
Overview
Distinguish external necessity, strong obligation, prohibition and advice using have to, must and should.
Form and rules
Have to often expresses rules or circumstances outside the speaker: I have to wear a uniform.
Must often expresses a strong personal obligation or a strong written/spoken rule.
Mustn't means prohibition; don't have to means lack of necessity.
Should/shouldn't gives advice or says what is a good/bad idea and is usually weaker than must.
Use had to for past obligation and will have to for future necessity.
A closer look
Should/shouldn't gives advice or says what is a good/bad idea and is usually weaker than must.
Use had to for past obligation and will have to for future necessity.
Examples
I have to submit the form by Friday.
You must keep this door closed.
You don't have to bring a laptop.
You mustn't park here.
You should back up your files.
Common mistakes
Immigration rules create an external necessity, so have to is the clearest choice.
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.