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: permission, obligation, prohibition & necessity
Choose the correct option to complete each sentence 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: permission, obligation, prohibition & necessity
Choose the correct options for the gaps in these sentences.
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: permission, obligation, prohibition & necessity
Rewrite the second part of the sentence without repeating the verb or verb phrase. Include ‘to’ when it is required. Don’t include ‘to’ when it can be dropped.
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.