#1 is the slang for "may I."
"Can I" really asks "Am I able..."
#2 is the one asking permission.
#3 is not often used, yes, and it's used more in situations when someone is really cautious around whoever's being asked the question.
1. Can I open the window?
2. May I open the window?
3. Might I open the window?
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Which one is common? Is #2 more polite than #1? Can we use #1 when we talk to elderly people? #3 rarely seems to be used. When can we use #3?
2 answers
Could I open the window.