Use can for ability ("I can swim") and for everyday permission ("Can I sit here?"). Use may for formal permission ("You may be seated") and for possibility ("It may rain"). Both words grant permission in modern English, so "Can I leave?" and "May I leave?" are both correct — may is just more formal. The old classroom rule that can means only ability is a myth: can has expressed permission for well over a hundred years and is accepted by every major usage guide.
The confusion clears up once you see that can and may divide three separate tasks between them:
Notice that may never covers ability. Swap it into "She can play the violin" and you get "She may play the violin" — which no longer means she is able to; it now means perhaps she will.
Can is the natural word for what someone or something is able to do:
In relaxed, everyday speech, can also asks for and gives permission. This is completely standard English:
May grants or requests permission in formal, polite, or official settings — signs, ceremonies, rules, and customer service:
May also expresses possibility — something that perhaps is true, or perhaps will happen:
Generations of pupils have heard a teacher answer "Can I go to the bathroom?" with "I don't know — can you?" The joke assumes can means only ability, so the "correct" request must be "May I?" It is a memorable nudge towards formal register, but as a rule of grammar it is simply wrong. Using can to ask permission is standard, respectable English recorded since the 1800s and endorsed by Merriam-Webster, Fowler's, and Garner's. The honest guidance is about tone, not correctness: choose may when you want to sound formal or extra-polite, and can everywhere else.
"You may not leave" can mean I forbid you to leave (permission) or perhaps you won't leave (possibility). In speech, stress settles it — a hard "may not" signals prohibition. In writing, use might not when you mean pure possibility: "She might not come" can only mean perhaps she won't.
Both flag possibility, but they aren't identical. May is about a specific occasion ("The parcel may arrive today"); can is about what happens from time to time or in principle ("Parcels can arrive damaged"). Warning labels use both: "may cause drowsiness" (it might, for you, now) versus "can be fatal" (it has that capacity).
Cannot (or can't) denies ability or permission: "You can't park here." May not denies formal permission: "Visitors may not enter." Note that there is no everyday contraction for may not — "mayn't" is archaic — so may not is always written in full.
Requests grow more formal along this line: Can I…? (casual) → Could I…? (softer, very common) → May I…? (formal, polite) → Might I…? (very formal, almost deferential). Could and might are the past-tense forms of can and may, but here they work as gentle, present-day softeners.
In elevated or set phrases, may expresses a wish or hope: "May the best team win," "Long may she reign," "Come what may." Can never does this job.
Two Cs and two Ms. Can is about being Capable — if you can replace it with "am able to," can is right. And May is More formal — reach for it when you'd also say "please." A scrap of history backs this up: may once meant "to be able," which is why the noun might means "power" — but modern English has handed ability over to can.
Barely. British and American English follow the same split: can for ability and informal permission, may for formal permission and possibility, with can-for-permission fully standard on both sides of the Atlantic. Very formal British writing may lean on may a little more, and American speakers can find an insisted-upon may slightly stiff — but these are matters of flavour, not different rules. Wherever you are, "Can I…?" is correct, and "May I…?" is the dressier option.
Both are correct. "May I…?" is the more formal, polite choice, favoured in official or respectful settings, while "Can I…?" is perfectly standard in everyday speech. The belief that "Can I…?" is a grammatical error is a myth — it has been accepted English for over a century. Choose based on how formal you want to sound.
No. In modern English, ability belongs to "can": "She can drive." If you say "She may drive," you have changed the meaning to permission (she's allowed to) or possibility (perhaps she will). Curiously, "may" once meant "to be able" centuries ago — a sense that survives only in the noun "might," meaning power or strength.
"May" describes a specific, one-off possibility: "It may rain this afternoon" (perhaps it will). "Can" describes a general or repeated one: "It can rain heavily here in spring" (it sometimes does). So "may" is about this particular occasion, while "can" is about what happens from time to time or in principle.
Both work. "May not" gives a formal prohibition: "Guests may not enter the kitchen." "Cannot" (or "can't") is plainer and just as correct: "Guests can't enter the kitchen." Be aware that "may not" can also signal possibility ("She may not come" = perhaps she won't), so context or spoken stress must make your meaning clear.
Yes. For permission, "may" carries a formal, polite, or authoritative tone — think ceremonies, signage, and rules ("You may now be seated"). "Can" is the everyday equivalent and sounds more relaxed. Neither is more "correct"; they differ in register. In casual conversation, an insisted-upon "may" can even sound stiff or old-fashioned.
