"Can" vs "May": Permission and Ability Difference
Can vs may explained with ability, permission, possibility, formal usage, common mistakes, exam traps, and practice questions.
A classic classroom correction goes like this:
Student: Can I leave the room?
Teacher: You can, but may you?
The joke is old, but the grammar point is useful. Can mainly talks about ability or practical possibility. May mainly talks about permission or formal possibility. In everyday English, people often use “can” for permission too, but exams and formal writing still expect you to notice the difference.
- Can = ability, capacity, or practical possibility.
- May = permission, polite/formal permission, or uncertain possibility.
Rule box: Use can for ability. Use may for permission in formal contexts.
Compare:
He can speak three languages.
May I speak now?
The first sentence asks about ability. The second asks for permission.
“Can” and “may” are modal verbs. They follow the same basic modal pattern:
| Pattern | Example |
|---|---|
| subject + modal + base verb | She can solve the problem. |
| modal + subject + base verb | May I enter? |
| subject + modal + not + base verb | Students may not enter without permission. |
Important: after a modal verb, use the base form of the main verb.
Correct: He can speak English.
Incorrect:He can speaks English.
| Use | Better Modal | Example |
|---|---|---|
| Ability | can | I can swim. |
| Informal permission | can | Can I borrow your pen? |
| Formal permission | may | May I leave early? |
| Rule-based prohibition | may not | Visitors may not enter this area. |
| General possibility | can | Accidents can happen anywhere. |
| Uncertain possibility | may | It may rain tonight. |
Use this method when choosing between “can” and “may”:
- Is the sentence about ability or skill? Use can.
- Is it asking or giving permission formally? Use may.
- Is it casual spoken permission? Can is acceptable in modern usage.
- Is it a rule, notice, or instruction? Prefer may or may not.
- Is it about possibility? Use can for general possibility and may for uncertain possibility.
___ you swim across the river?
This is ability. Correct: Can you swim across the river?
___ I submit the form tomorrow, sir?
This is formal permission. Correct: May I submit the form tomorrow, sir?
Students ___ not enter without an identity card.
This is rule-based prohibition. Correct: Students may not enter without an identity card.
-
Can you swim?
Ability is being tested. -
May I come in?
Formal permission is being requested. -
Can I leave now?
Informal permission; common in speech. -
May I leave now?
More formal and polite. -
He can speak three languages.
Ability, not permission. -
Students may not enter without permission.
Rule-based prohibition. -
Anyone can make mistakes.
General possibility. -
She may arrive late because of traffic.
Uncertain possibility. -
This medicine can cause drowsiness.
General possible effect. -
The principal said we may use the hall after lunch.
Permission was granted.
Incorrect: May you swim?
Correct: Can you swim?
“May you…?” is not the normal way to ask about ability. It can appear in blessings such as “May you succeed,” but that is a different structure.
In conversation, “Can I leave?” is normal. But in formal grammar questions, especially when the meaning is clearly permission, may is safer.
Informal: Can I leave?
Formal: May I leave?
- May not = not allowed.
- Cannot / can’t = unable, impossible, or not allowed depending on context.
You may not park here. = You are not permitted.
I cannot lift this box. = I am not able.
Use can for what is generally possible:
Too much sugar can harm your health.
Use may for what is possibly true in a particular situation:
The train may be late today.
“Cannot” is normally written as one word. “Can not” is possible only when “not” belongs to a separate contrast, but that is rare.
Correct: I cannot attend the meeting.
Also common: I can’t attend the meeting.
| Incorrect | Correct | Why |
|---|---|---|
| May you swim? | Can you swim? | Ability needs can. |
| He may speak three languages. | He can speak three languages. | Skill/ability. |
| Students can not enter without permission. | Students may not enter without permission. | Formal prohibition. |
| Can I speak, Your Honour? | May I speak, Your Honour? | Formal permission. |
| She can goes now. | She can go now. | Modal + base verb. |
| It can rain tonight. | It may rain tonight. | Specific uncertain possibility. |
Choose the correct option.
- ___ you solve this puzzle? (Can/May)
- ___ I use your phone, please? (Can/May)
- Visitors ___ not touch the exhibits. (cannot/may not)
- He ___ play the violin beautifully. (can/may)
Find and correct the error.
- May you drive a car?
- Students can not enter the lab without a pass.
- She can speaks French.
Rewrite or fill in the blank.
- Make this more formal: Can I leave the room?
- Fill in: The road ___ be closed because of repairs. (can/may)
- Fill in: A small mistake ___ change the meaning of a sentence. (can/may)
- Can — ability.
- May — polite permission; “can” is also common informally.
- may not — rule/prohibition.
- can — ability.
- Can you drive a car?
- Students may not enter the lab without a pass.
- She can speak French.
- May I leave the room?
- may — uncertain possibility in a specific situation.
- can — general possibility.
Can = ability or practical/general possibility.
May = formal permission or uncertain possibility.
Memory trick: Can = capacity. May = permission.
Revision examples:
Can you swim?
May I leave now?
Students may not enter without permission.