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"Can" expresses ability or capacity (to be able to do something); "may" expresses formal permission or possibility (something might happen).
Side-by-side comparison
"Can" expresses ability or asks for permission in a casual, direct way. It is the most common option in everyday conversations.
She can play the piano beautifully, she has been taking lessons since she was four years old.
Can you help me move this table? It is heavier than it looks.
The traffic on that road can be terrible on Friday afternoons. I suggest taking the highway instead.
"May" is more formal. Use it to give or ask for permission in serious contexts, or to express possibility with a more careful tone. "May I...?" sounds more polite than "Can I...?".
May I ask what time the meeting is scheduled for? I want to make sure I am not late.
The patient may experience some mild discomfort after the procedure, but it should pass within 24 hours.
You may use the conference room until 3 p.m., but it will be needed for a client meeting after that.
Common mistake
- •The school rule "can = ability, may = permission" is a 19th-century prescriptivist rule that does not reflect modern English: "Can I go to the bathroom?" is completely accepted even in formal contexts.
- •The distinction that does matter is for possibility: "may rain" is more precise than "can rain" for expressing future possibility.
Trick to remember it
- •Modern rule: "can" = ability or informal permission.
- •"May" = future possibility ("it is possible that") or very formal permission.
- •"It may rain tomorrow" expresses a more specific possibility than "it can rain tomorrow".
Quick rule
- •"Can" = ability and informal permission.
- •"May" = future possibility and formal or written permission.
- •For everyday permission, "can" is completely valid.
Did you know?
The correction "do not say can, say may for permission" was popularised by Lindley Murray's grammar books (1745-1826), the best-selling textbooks in the history of English for over 100 years. Murray, an American Quaker lawyer retired in York, England, based his rules on Latin logic rather than actual English usage. His influence was so massive that his rules continue to appear in textbooks nearly 200 years later, long after linguists showed they were never descriptively accurate.
Practise what you learned
Exercise 1 · Pick the right one
She _____ speak four languages. She was raised in Europe.
Exercise 2 · Pick the right one
"_____ I use your phone for a second? Mine is out of battery."
Exercise 3 · Form the word
Related word pairs
"Been" is the past participle of "be" (used with have/has/had); "being" is the present participle of "be" (used with am/is/are/was/were).
'Could' expresses reasonable possibility or polite permission; 'might' expresses more remote or uncertain possibility.
"May" expresses higher probability or formal permission; "might" expresses lower probability or is the past tense of "may".
'May well' expresses high probability; 'might well' expresses reasonable possibility with slightly more uncertainty.
Bryan López
Founder of SpeakUP Academy