Using Can i, May i, Could i

Can I..?

"Can I...?" is the most casual way to ask for permission. It's common for talking to friends, coworkers, and family members:

Ø Can I see it?

Ø Can I get something to drink?

May I...?

"May I...?" is the most formal way to ask for permission in English. Formal language is useful for talking to strangers and when there's a large power gap between you and the person you're talking to.

You can ask a stranger for a small favor like this:

Ø  May I borrow your pen for a second? 

    Some teachers in elementary, junior high, and high school require their students to ask for permission using     "May I...?"

Student: Can I go to the bathroom?

Teacher: "May I...?"

Student: May I go to the bathroom?

Teacher: Yes, you may.

Could I...?

"Could I...?" is a good way to ask for permission when you need to ask for something that's a "bigger" request. In other words, you don't feel as comfortable asking for it. For example, you might ask your sister:

      Ø  Could I borrow your other car when I'm in town?

"Could I...?" is not as formal as "May I...?" but it's better for big requests.