Although, traditionally, can has meant “to be able” and may has meant “to be permitted” or to express possibility, both can and may are commonly used interchangeably (especially in spoken, informal language) in respect to permission. Even the Oxford English dictionary informs us that the permission use of can is not incorrect, but it’s better and more polite to use may in formal situations.
Example: He can hold his breath for 30 seconds.
Meaning: He is able to hold his breath for 30 seconds.
Example: He may hold his breath for 30 seconds.
Meaning #1: It is possible that he will hold his breath.
Meaning #2: He has permission to hold his breath. (This meaning is unlikely.)
Example: May/Can I go to the mall tonight?
Regardless of whether you choose can or may here, it is clear that permission is being requested.
In spoken English, a request for permission is generally answered with can, cannot, or can’t, rather than with may or may not, even if the question was formed using may. (Although mayn’t is a word, it looks and sounds strange even to native speakers.)
Example of Dialogue:
“May I go to the mall tonight?”
“No, you can’t/cannot go.” OR “Yes, you can go.”
Occasionally, you may hear someone say something like, “I cannot but argue when you say such silly things.” The expression cannot but argue is actually an old-fashioned way of saying “cannot help arguing.” You may also hear the expression can but, which means “can only.”
Example: We can but do our best to arrive on time.
1. Can/May you imagine a world without war?
2. Can/May I call you for a date?
3. She can/may run faster than anyone else on the team. (able to)
Pop Quiz Answers
1. Can you imagine a world without war?
2. Can OR May I call you for a date?
3. She can run faster than anyone else on the team.