In this context, I always think of "
can" and "
may"
Some years ago, I was on a Tube train in London with my then boss; we were standing in the aisle between the seats near the doors because we were due to change at the next station.
A very attractive woman got on and said to my boss "
Can I get past?"
My boss looked at the backpack on the floor at her feet, turned to the woman and replied "
No."
The woman then retorted angrily "
I said can I get past please?" to which my boss smiled sweetly and answered "
I know exactly what you said; I believe that what you meant to say was MAY I get past PLEASE?" as she leant backwards to let the woman scramble past. I was hugely embarrassed by the whole exchange.
We got off at the next stop and I asked my boss why she had been so pedantic. She said that if the woman had said please in the first place she would have let it go but that the combination of bad manners and ignorance had annoyed her.
I have never forgotten that lesson - it is remarkable how much leeway you can gain with a show of manners