Modals of Obligation, Permission & Prohibition
At B2 you handle the finer distinctions between modal verbs of obligation, permission and prohibition — including the difference between external rules and personal opinion, and the tricky contrast between…
At B2 you handle the finer distinctions between modal verbs of obligation, permission and prohibition — including the difference between external rules and personal opinion, and the tricky contrast between mustn’t and don’t have to.
Obligation & necessity
| Modal | Meaning | Example |
|---|---|---|
| must | strong obligation (often the speaker’s own) | I must finish this today. |
| have to | obligation from outside (rules) | You have to wear a seatbelt. |
| have got to | informal obligation | I‘ve got to go now. |
| should / ought to | advice, weaker obligation | You should rest. |
| be supposed to | expected (but maybe not done) | We‘re supposed to arrive by 9. |
Prohibition vs no obligation
| Modal | Meaning | Example |
|---|---|---|
| mustn’t | prohibition — it’s not allowed | You mustn’t smoke here. |
| don’t have to | no obligation — it’s optional | You don’t have to come. |
| can’t / not allowed to | prohibition (rules) | You can’t park here. |
The classic trap: mustn’t ≠ don’t have to“You mustn’t tell anyone” = it is forbidden. “You don’t have to tell anyone” = you can if you want, but it’s not required. They are almost opposites — never swap them.
Examples from EduCareer
- Students have to submit homework online. (school rule)
- You don’t have to buy the book — it’s optional.
- You mustn’t use a dictionary during the test.
Tutor tip for Arabic speakersFor past obligation, “must” has no past form — use had to: “I had to wait,” not “I must waited.” And remember the negative split: prohibition = mustn’t; absence of obligation = didn’t have to.
Common mistakes
- You don’t have to smoke here (= forbidden). → You mustn’t smoke here.
- Yesterday I must wait an hour. → Yesterday I had to wait an hour.
- She must to leave early. → She must leave early.
Practise with the 20 questions below.
Check your understanding
Answer the questions below. You will see instantly if you are right.
1."You ___ smoke here — it's forbidden."
prohibition → mustn't.
2."You ___ come if you're busy — it's optional."
no obligation → don't have to.
3."Drivers ___ wear a seatbelt." (law)
external rule → have to / must.
4.Past of 'must' (obligation) is:
had to.
5."Yesterday I ___ wait an hour."
past obligation → had to.
6.Which is correct?
must + base verb, no 'to'.
7."We ___ arrive by 9, but we're often late."
expectation → be supposed to.
8."You ___ use your phone in the exam." (banned)
prohibition → mustn't.
9.'have got to' is mainly:
informal obligation.
10."You ___ see a doctor about that cough." (advice)
advice → should/ought to.
11."I ___ pay for the ticket — my friend treated me."
no obligation (past) → didn't have to.
12.'mustn't' and 'don't have to' are:
forbidden vs optional.
13."Guests ___ check out by 11am." (hotel rule)
external rule → have to.
14."You ___ to apologise; it wasn't your fault."
no obligation → don't have to.
15."Visitors ___ feed the animals." (forbidden sign)
prohibition → must not.
16."He ___ work last weekend." (was obliged)
past obligation → had to.
17."Strictly, you ___ be 18 to enter."
rule → have to.
18."You ___ worry — everything's handled."
reassurance, no need → don't have to (or needn't).
19.'be supposed to' suggests:
expectation that may not be met.
20."Candidates ___ talk during the test." (rule, forbidden)
prohibition → must not.
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