Lesson

Must and have (got) to

Strong obligation

≈ 15 min 8 block(s)

Text

Must and have (got) to

This lesson explains how to use must, mustn't, have to, have got to, don't have to and had to to express obligation, necessity and prohibition in English.

  • Must and have to both express obligation, but they are used differently.
  • Must often expresses the speaker's strong personal obligation or logical necessity.
  • Have to (or have got to) usually shows an external obligation (rules, laws, employer).
  • Mustn't expresses prohibition. Don't have to indicates no obligation.

Table

Must vs Have (got) to — Quick Reference

Form Meaning Example
must Speaker's strong obligation / logical necessity You must submit the report by Friday.
mustn't Prohibition (not allowed) You mustn't share your password.
have to / has to External obligation (rules, employer, law) Employees have to wear ID badges.
have got to / has got to Informal: strong obligation (similar to have to) I've got to finish this presentation.
don't have to / doesn't have to No obligation (it's optional) You don't have to attend the meeting if you're on leave.
had to Past obligation She had to work late yesterday.

Tip

Key rule: speaker vs external obligation

Remember the main difference:

  • Use must when the speaker expresses a personal obligation, a strong recommendation, or a logical conclusion: I must, we must.
  • Use have to (has to for third person singular) for obligations imposed by an external authority or situation: She has to, They have to.
  • Have got to is informal and used like have to in spoken English.
  • Don't have to means there is no obligation; mustn't means something is forbidden.

Check subject and tense: must doesn't change with -s, but have → has in third person; past forms use had to.

Example

Examples in context

You must submit the financial report by Friday.

All staff have to complete the security training this month.

I've got to call the client before noon.

You don't have to attend the optional workshop.

Tip

Common mistakes

Watch out for these frequent errors:

  • Confusing must and have to — decide if the obligation is personal (must) or external (have to).
  • Adding -s to must in the third person (incorrect: He musts) — must does not change form.
  • Using mustn't when you mean don't have to — mustn't = forbidden, don't have to = optional.
  • Forgetting the 'to' after have (incorrect: She have go) — correct: have to / has to.
  • Incorrect negative or question forms (e.g., 'Mustn't you...?' is rare; prefer 'Don't you have to...?').

Check verb forms, subject agreement and whether the situation is a rule or a personal decision.

Quiz

Choose the correct sentence:

Hint: Check subject-verb agreement and the correct form for obligation with he/she.

Quiz

Complete: Employees _____ wear safety boots on the site.

Hint: Think about rules set by the company or location.

Quiz

Choose the best option to complete the sentence: You _____ smoke in the office.

Hint: Decide if the sentence is forbidding an action or saying it is optional.

Key Points

GrammarPoint

must

modal verb CEFR B1 //mʌst//

Expresses strong personal obligation or logical necessity.

I must finish the proposal tonight.

GrammarPoint

have to

semi-modal / verb phrase CEFR B1 //hæv tuː//

Indicates obligation imposed by external factors (rules, employer).

We have to follow the company's security procedures.

Expression

have got to

expression / semi-modal CEFR B2 //hæv ɡɒt tuː//

Informal form similar to have to; expresses strong necessity.

I've got to finish these slides before the meeting.

GrammarPoint

mustn't

modal verb (negative) CEFR B1 //ˈmʌsənt//

Expresses prohibition — something is not allowed.

You mustn't use your phone during the exam.

GrammarPoint

don't have to

phrase CEFR B1 //doʊnt hæv tuː//

Indicates no obligation; something is optional.

You don't have to come if you are busy.

GrammarPoint

had to

verb phrase CEFR B1 //hæd tuː//

Past form indicating an obligation in the past.

I had to work late last week.