Must, Have To, and Should: Obligation, Rules, and Advice

Must, have to and should express different levels and sources of obligation. Choosing the right form depends on whether you mean a rule, an external necessity, no necessity or advice.

Must: strong requirement

Use must for a strong rule or necessity.

• You must wear a seat belt.
• I must remember to send the document.
• Students must not share passwords.

Mustn’t means something is prohibited.

Have to: external necessity

Have to often describes a requirement created by work, law, schedules or circumstances.

• I have to submit the form by Friday.
• She has to start at eight.
• Do we have to bring our passports?

Should: advice

Should recommends what is sensible or helpful.

• You should practise speaking every day.
• We should leave before the traffic gets heavy.

Mustn’t vs don’t have to

You mustn’t use your phone. = prohibited.

You don’t have to use your phone. = not necessary.

Past and future

Use had to for past obligation and will have to for many future obligations.

Practice

1. You ___ not enter without permission.
2. I ___ finish this because the deadline is tomorrow.
3. You look tired. You ___ take a break.
4. We ___ work last Saturday.

Answers: 1. must; 2. have to; 3. should; 4. had to.