Masarah: When I went to school I was taught
that when asking for something you use
"may I (have/do something)". "Can" was
used only when asking if you are
"physically capable" of something.
You're not old enough, Masarah, for that to have been a fact. It was a piece of fiction that you were taught then and it is a piece of fiction that is still being taught today.
This, below, from the 1828 edition of Websters Dictionary:
- To be possible. Nicodemus said, How can these thing be? John 3.
- To be able; to have sufficient strength or physical power. One man
can lift a weight which another can
not. A horse can run a certain
distance in a given time.
Even the definition and meanings for 'to be able', can be glossed/understood as "it is possible that ... "
"Can I", used for permission, expresses exactly the same thing that 'may' expresses, ie. "Is it possible for me to ..." It has nothing to do with ability/capability. That was a fatuous notion made up by someone who had no idea of the meanings that the modal verb 'can' has/has had in English.
Back in 1828, 'can', as this entry shows, had the meaning of permissable.
- To have just or legal competent power, that is, right; to be free from
any restraint of moral, civil or
political obligation, or from any
positive prohibition. We can use a
highway for travel, for this is
permitted by law. A man can or cannot
hold an office. The Jews could not eat
certain kinds of animals which were
declared to be unclean. The House of
Commons in England can impeach, but
the House of Lords only can try
impeachments. In general, we can do
whatever neither the laws of God nor
of man forbid.
All anyone had/has to do was/is consult a dictionary to know that this idea is false.
Yes, 'may' is more polite, but people who demand this level of politeness, even for children, for all situations, are not being realistic for they don't demand that same level of politeness for all other situations. Nor do they demand that the even more polite, 'might' be used.
As soon as these folks have corrected their kids, or someone else, they turn around and use 'can' to ask permission of others. As with so many fatuous rules, they are trying to enforce a myth, a prescription. Kids are bright enough to realize this which is why prescriptions/myths simply don't take. They are, as Steven Pinker says, "bits of folklore that originated for screwball reasons several hundred years ago and have perpetuated themselves ever since".