Modals for permission, obligation, prohibition & necessity
B2 • quick reference
Permission: can, could, may, might
| Function | Natural patterns | Register |
|---|---|---|
| Asking | Can/Could I … ?, May/Might I … ? | can informal • could more polite • may/might formal |
| Giving | You can … / You may … | can neutral • may official |
| Refusing | You can’t … / You may not … | may not is formal/official |
Past permission: use was/were allowed to. The affirmative could is not used for one-off permission in the past (He was allowed to leave, not *He could leave for that specific occasion).
Alternatives to modal (permission/possibility)
| Form | Use | Example |
|---|---|---|
| be allowed to | rules & policies | Employees are allowed to work remotely. |
| be permitted to | formal/official | It is not permitted to photograph the exhibits. |
| be able to | possibility/ability in any tense | You won’t be able to submit after midnight. |
Avoid It is allowed to… in most contexts. Prefer You are allowed to… or … is allowed.
Obligation: must vs have to
- must = speaker’s view/strong internal obligation: I must stop smoking.
- have to = external requirement (rules, schedule, doctor): I have to stop smoking.
- Past/other tenses typically use have to: I had to cancel, I’ll have to leave.
- Informal British English: have got to = strong obligation now: I’ve got to go.
Prohibition vs. no obligation
| Meaning | Form | Example |
|---|---|---|
| Prohibited | mustn’t + base | You mustn’t share client data. |
| Not necessary | don’t/doesn’t have to + base / don’t/doesn’t need to + base | You don’t have to arrive before 7. |
Mustn’t ≠ don’t have to. The first bans an action; the second removes the need.
Necessity & lack of necessity
| Time | Positive necessity | Absence of necessity | Example |
|---|---|---|---|
| General / now | need to / have to | don’t need to / don’t have to | We need to confirm by Friday; you don’t need to call today. |
| Specific occasion (now/future) | — | needn’t + base | You needn’t wash up; I’ll do it. |
| Past (not done) | had to | didn’t need to + base | I didn’t need to queue because I had a pass. |
| Past (done unnecessarily) | — | needn’t have + past participle | You needn’t have bought flowers (but you did). |
Use didn’t need to when the action was not necessary and was not done; use needn’t have + V-ed when it turned out unnecessary but the action happened.
Be supposed/meant to & had better
- be supposed/meant to + base — expected/required by rules or plans: We’re supposed to check in an hour before take-off. Negative = not allowed/against expectations: You aren’t meant to park here.
- ’d better (not) + base — strong advice with an implied negative result: You’d better save your work / You’d better not be late. (No hadn’t better.)
At a glance
- Permission — can/could/may/might; past: was/were allowed to; official notices: be permitted to.
- Obligation — must (speaker’s), have to (external). Other tenses: have to/had to. Informal: have got to.
- Prohibition — mustn’t. Not necessary — don’t have to / don’t need to.
- Necessity — general: need to / have to; specific “not necessary now”: needn’t; past contrast: didn’t need to vs needn’t have + V-ed.
Exercises:
Modals for permission, obligation, prohibition, and necessity
Choose the correct option to complete the sentences below.
1
Students
their proposals until Friday.
2
Employees
their passwords under any circumstances.
3
You
your own towels; the hotel provides them.
4
You
so much bread — we already had plenty.
5
All visitors
a badge at all times.
6
Staff
expenses within 30 days.
7
I’ve finished my tasks —
early today?
8
Visitors
photos in the gallery if the flash is off.
9
You
your visa before it expires.
10
Passengers
liquids over 100 ml through security.
Modals for permission, obligation, prohibition, and necessity
Instruction: For each sentence, choose two options that are correct in meaning and form.
1
At this museum, visitors ____ take photos. permission
A.
B.
C.
D.
2
Employees ____ smoke in the building. prohibition
A.
B.
C.
D.
3
You ____ bring your passport to the interview—any ID is fine. no necessity
A.
B.
C.
D.
4
All staff ____ wear their badges at all times. obligation
A.
B.
C.
D.
5
The roads were empty, so we ____ hurry. no necessity in the past
A.
B.
C.
D.
6
When I was a kid, we ____ stay up late on Fridays. past permission
A.
B.
C.
D.
7
____ I leave a bit early today? asking permission
A.
B.
C.
D.
8
You ____ park here—it's a fire lane. prohibition
A.
B.
C.
D.
9
To access the secure server, you ____ change your password every 90 days. necessity
A.
B.
C.
D.
10
During the exam, we ____ use our phones. past prohibition
A.
B.
C.
D.
Modals for permission, obligation, prohibition, and necessity
Fill in each gap with one suitable word or two contracted words (e.g. shouldn’t, mustn’t, needn’t or similar).
1
You wear a helmet on this site at all times.
2
You use your phone during the exam.
3
I open the window for some fresh air?
4
You bring a dessert; there is plenty of food.
5
You check the cables first — it often fixes the issue.
6
All visitors sign in at reception.
7
Employees work overtime unless they volunteer.
8
You smoke anywhere in this building; please go outside.
9
I borrow your charger for a minute?
10
Students submit the form by Friday to be eligible.