In school when we had to ask the teacher for permission to use the toilets, a lot of my friends typically asked, “Miss, can I go to the toilet?” More often that not the teacher answered in the affirmative, but this once a very grumpy English teacher told my friend, “You can, but you may not.”Now I never liked this teacher much. She taught us a lot of wrong pronunciation. That aside, was my friend really wrong when she used the word “can” instead of “may”?I wouldn’t say so, you know. Typically, you use the word “can” in the following instances:
1. Talking about what is probable or possible, like,
I am not sure but Kate can make a good queen someday.
2. Talking about ability:
You can use my phone.
3. In requests:
Can you help me with the homework?
4. When you sense what is happening now:
I can see them across the street
I believe that when the teacher denied permission to my friend, she assumed that the “can” meant “ability”. Now “may” has its place here, because the student – teacher relationship is essentially formal, and the more prissy “may” does way better in terms of seeking permission. But English being the rapidly morphing language, I think it is acceptable now to replace “may” with “can” in informal conversations. So yes, you can say “Can I borrow your pen?” or “Can I go to the party with you?” without feeling completely out of place.
You know much as I try to follow some kind of logic for it, English I think, is a language that works a great deal according to the way things sound to you. So if I had to knock on your door, I’d probably say “May I come in?” although saying “Can I come in?” is also accepted now. I’d say that because it just sounds better. Likewise, if I needed a lift from you, I’d probably ask “Can I get a lift?” Again, this sounds way better than “May I get a lift?”
So now you may go to the toilet and think about this. My advice would still be, in a formal environment, use “may” and among friends, informally, use “can”. I told you, it’s all about how it sounds.