I'm making a record of this little exchange because it illustrates a question that comes up frequently--the difference between "usage" and "correctness." The discussion started when a student in class asked which of these is correct:

Who of you…

Which (ones) of you…

…have been to England? (for example).

My first inclination was (and still is) to say "How many of you…" but it could be that you want to know which individuals, in which you have to say it one of these ways, or

Who among(st) of you have been to England?

But as often happens, the more I thought about it, the stranger all of these expressions sounded! I told the class I'd have to give it some thought, or at least give my brain a little rest and come back to it later.

Later I wrote:

> Sorry for the glitch. I don't know why "who of you" sounded awkward;
> maybe I had "who among you" in the back of my mind, which is in fact
> more common. Maybe it's just the rhyming that jarred. Google can be
> an excellent corpus (like a huge searchable text) for this sort of
> thing. I got 92,000 hits for "who of you" and 103,000 for "who among
> you," 18,200 for "who amongst you" (more British).
>
> In sum, "which (one/s) of you, who of you, who among(st) you" are all
> acceptable, in writing also.

To this an enterprising student replied:

> Hi!
> Don't know if this (the posting) works well...However, this is what my
> English friend wrote:
>
> The correct grammar is "Which one of you" . You could say
> "Who amongst you is..." but it is a clumsy way. You can never say "Who
> of you" and be correct. Hope that clarifies everything. So if I were
> to ask "which one of you.. or which of you"( implying more than one) I
> would have to say "you were all wrong!!"
>
> Now, I am confused again...

My reply to this was:

Thanks for pursuing this point. It is an excellent example
of a fact that all English teachers should have written behind their
ears, which is that usage is not fixed. There are many grey areas,
and many variables, e.g., of register (degree of formality) and
dialect (national, regional).

This is why some dictionaries have "usage panels," such as the one
that advised the American Heritage dictionary at bartleby.com (to
which most of the index of links on my homepage refer). I couldn't
find anything about this, though.

What is "usage"? It is the way people talk or write. What people?
When? Answer both these questions and you have an insight into what
the usage of a word, phrase, or grammatical structure is.

"Correctness" is a different concept. "Correctness" assumes 1) that
usage has been clearly described, and 2) that a respectable body of
advisers (e.g., a usage panel) has made a pronouncement about what
usage is "preferred" in various contexts.

So you can see that, because there ARE grey areas, almost anyone's
opinion of what is "correct" or not is questionable (even that of
usage panels), and the people you should trust LEAST are the people
who are the readiest to tell you what is "correct" or "not correct,"
because more often than not, if the question has come up it means the
answer is uncertain, that this is one of the grey areas of usage, and
therefore any simplistic answer will be wrong.

There are many cases where everyone would agree, e.g, is "ain't"
correct (even though you might hear it a lot), or "he don't"? But
that's one extreme, and there are many other cases where the answer
cannot be so cut and dried.

If you are going to be an English teacher, you will be well advised to
understand and accept this point, and try to help your students
understand it, too (as I am doing now!). It's not easy, because too
many people expect black-and-white answers to all their questions, and
become frustrated when they don't get them. It requires more
self-confidence, not less--especially as a non-native speaker, to
admit something you are not sure of. Another word for this is
"honesty"--although in the area of language, especially, people are
subjected to so much false information based on presumed "authorities"
(dictionaries, teachers) in school (in their native language as well
as in foreign languages) that often people might be honest but in
truth are simply passing on something they have heard or read
elsewhere that they are assuming is "correct."

If you ever study linguistics, these are things, basic characteristics
of language, that you will learn, or should learn.

Now, returning to the issue at hand, I stand by my conclusion below.
But please continue your research, and thanks for your stimulating
questions!