What you'll learn
By the end of this lesson, you'll be able to express obligation at different levels of formality and force.
When do I use it?
Choose the strength and formality of your obligation:
- Personal/internal: "I must finish this today." (I feel I have to)
- External/general: "You have to wear a uniform." (a rule)
- Official/formal: "Staff are required to sign in." "Employees must not use phones."
- Very strong/legal: "be obliged to", "be compelled to": "You are obliged to declare your income."
Use "don't have to" (optional) vs "mustn't" (forbidden) — they are not the same.
How do I form it?
must / have to + base verb be required / obliged + to + verb mustn't (prohibition) vs don't have to (optional)
- I must apologise for the delay.
- All guests are required to register at reception.
- You don't have to bring anything.
- You mustn't smoke in the building.
Common mistakes for Spanish speakers
"Tengo que" → "I have to"; "debo" → "I must" — but in the negative the meanings split: "no tengo que" = "I don't have to" (optional), while "I mustn't" = prohibition. Speakers also say "I must to go" (no "to") and "have to" gets an extra "to": "have to to go" is wrong. For the past, "must" has no past — use "had to": "I had to wait", not "I must wait" about yesterday.
must = personal duty. have to = external rule. be required to = formal. had to = past obligation.
Practice
Multiple Choice
C1Which sentence means 'it's forbidden'?
Fill in the Blank
C1All visitors are required wear a badge.
Hint: be required + to + verb.
Find the Error
C1Multiple Choice
C1Which is the past form of 'must'?
Practice Speaking
Apply what you've learned in a real conversation with AI feedback.
Level: C1