What is Modal Must for Obligation?
Modal must is used to express strong duty, obligation or necessity — something that is mandatory or very important to do.
Must for obligation shows that something is necessary or mandatory: I must finish this work today. It's stronger than should and more formal than have to.
- •Legal requirement
- •Safety rule
- •Absolute necessity
- •Non-negotiable
- •External obligation
- •Advice or recommendation
- •Important but flexible
- •Can discuss
Step-by-step worked examples
You must wear a seatbelt while driving.
Modal: must Form: must + base verb (wear) Meaning: It is a legal requirement and non-negotiable
Students must submit their essays by Friday.
Modal: must Form: must + base verb (submit) Meaning: Deadline is mandatory, no exception
I must take my medicine every morning.
Modal: must Form: must + base verb (take) Meaning: It's necessary for health, non-negotiable
Flashcards
Quick quiz
Q1.Which sentence uses must correctly?
Q2.What does 'You must not eat before surgery' mean?
Q3.Choose the strongest obligation:
Q4.How do you express past obligation?
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Common mistakes
You must to go home now. — Correct: You must go home now. (No 'to' after must)
He musts study hard. — Correct: He must study hard. (Must never adds 's' for third person)
I must went to the hospital yesterday. — Correct: I had to go to the hospital yesterday. (Use 'had to' for past)
You mustn't eat after midnight is optional. — Correct: If it's optional, use 'don't have to': You don't have to eat after midnight.
FAQ
What is modal must for obligation?
Must expresses strong, mandatory obligation or duty — something that is non-negotiable and necessary to do.
What's the difference between must and have to?
Must shows personal necessity or legal requirement (stronger); 'have to' shows external obligation (slightly weaker, more colloquial).
Can you use must for past obligation?
No, must is present/future only. For past obligation, use 'had to': I had to work late yesterday.
What's the difference between mustn't and don't have to?
'Mustn't' = prohibition (you can't); 'don't have to' = not necessary (optional).