Obligation and Prohibition
A2 · ElementaryModal VerbsMust and have to say something is required — but their negatives, mustn't and don't have to, mean two very different things.
What you'll learn
- Must + base verb and have to + base verb both express obligation
- Mustn't means something is forbidden — don't do it
- Don't have to means something isn't necessary, but it's still allowed
- This mustn't vs. don't have to contrast is the key point of this lesson
Must and have to: saying something is required
Both must and have to express obligation — that something is necessary or required.
Mustn't vs. don't have to
This is the most important contrast in the lesson: mustn't means something is forbidden — you are not allowed to do it. Don't have to means the opposite kind of thing entirely: it's simply not required, but you're still free to do it if you want.
Forming questions
Have to forms questions with do/does, like a regular verb. Must can form questions directly, but in everyday speech, do you have to is far more common.
Real English
Watch out
Don't add to after must — it's followed directly by the base form of the verb.
Don't have to means something isn't necessary — it doesn't mean forbidden. Use mustn't for prohibition.
Have to behaves like a regular verb — it needs has with he/she/it.
Real life — House rules
"Do I have to take my shoes off?"
"No, you don't have to — but you're welcome to."
"Got it. Anything I definitely shouldn't do?"
"Just one thing — you mustn't feed the cat, she's on a special diet."
Practice
Exercise 1 · Choose the correct sentence
Choose the correct sentence — obligation.
Exercise 2 · Choose the correct sentence
Choose the correct sentence — obligation with have to.
Exercise 3 · Choose the correct sentence
Choose the correct sentence — prohibition (forbidden).
Exercise 4 · Choose the correct sentence
Choose the correct sentence — no obligation (optional, not forbidden).
Exercise 5 · Choose the correct question
Choose the correct question.
Exercise 6 · Choose the correct answer
Which means something is forbidden?
Exercise 7 · Choose the correct answer
Which means something is not necessary, but not forbidden either?
Exercise 8 · Choose the correct sentence
Choose the correct sentence.
Exercise 9 · Complete the sentence
Complete: 'You ___ (mustn't) park here — it's a fire exit.'
Exercise 10 · Complete the sentence
Complete: 'You ___ (not/have to) pay — entrance is free today.'
Exercise 11 · Sort into groups
0 / 6 sorted
Quick challenge
Five quick questions to check what stuck.
Question 1 / 5
Score: 0/0
Choose the correct sentence.
You learned
- Must and have to both express obligation.
- Mustn't means something is forbidden.
- Don't have to means something isn't necessary, but is still allowed.
- Have to forms questions and negatives with do/does, like a regular verb.
Related grammar lessons
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Modal Verbs of Ability
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Must vs. Have To
Learn the key grammatical difference between must and have to — must never changes form, so have to fills in the past, future, and question forms it can't reach.