must, have to, should

Level B1 · rules and advice

How do you talk about rules and advice?

These modal verbs show how strong something is: necessary (must / have to) or just a good idea (should). Their negatives mean very different things.

When you use it

Rules at work or school.
Giving advice to a friend.

Pattern

modal + base verb (no to, no -s)

Examples

You **should** see a doctor. — advice
You **mustn’t** smoke here. — not allowed

Watch out: don’t have to = not necessary; mustn’t = forbidden. They are not the same.

The rule

must / have to = it's necessary. should = it's a good idea. don't have to = it's not necessary; mustn't = it's not allowed.

Not necessary ≠ not allowed: You don't have to wear a tie. → You mustn't smoke here.

Common mistakes

Not: ~~You should to rest.~~ — But: You should rest.
Not: ~~She musts go.~~ — But: She must go.

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