When I was in school, I’d hear this phrase often from my English language teacher, when any of us–in her class–asked for permission. After so many years, it is still stuck in my head and every time someone asks “Can I borrow (so-and-so object)?” I jokingly reply “You can, but you may not!” Of course, those who understand smile back and rephrase the question, those who don’t, just look at me like I’m mental! However, it does beg the question: should you use ‘can’ or ‘may’ when asking something?

While the two words are used interchangeably, there is a subtle difference in meaning. ‘Can’ denotes ability and ‘May’ denotes permission. In informal situations, both can be used synonymously, however, in formal conversation and writing, both are distinct.

Here are some examples to help you understand better:

Ability:
Q) Can you finish your homework before dinner?
Q) Can he climb the stairs?

Permission:
Q) May I have dinner first and then watch T.V.?
Q) May we go out to play?

We are familiar with this opening line on customer service numbers, “Thank you for calling XYZ, how may I help you?”, some people are of the opinion, it sounds ‘scripted’ like the executive just wants to end the conversation before it even begins. Though monotonous and robotic, many customers do get offended if this line isn’t used. In situations where you don’t know the person well or, if the person is older than you, or is a stranger, using “May I?” is more appropriate.
When talking with family or a friend, it won’t be considered a crime if you say “Can I borrow this book?”, however, “May I borrow this book?” sounds a lot more polite. We all know English is a funny language, there are many rules which can be difficult to remember, in the end, it all comes down to, whether something sounds right. If it does, good for you, if it doesn’t you can always use alternative words or phrases.