The pronoun pair who/whom functions along the same lines as I/me, he/him, she/her, we/us, and they/them. Who is a subject form and whom is an object form.
For many English speakers and writers, whom has become an unnecessary word. Instead of using who as a subject and whom as an object, these speakers and writers use who as both subject and object, just as everyone uses you as both subject and object.
So far, so good. At this point in the development of English, using who as an object has become acceptable in standard English. Many speakers do choose to distinguish between who and whom in speech and/or writing, but using who alone is perfectly all right.
ERROR ALERT: The usage problem that exists with who/whom is not a failure to use whom as an object. It is the error of using whom as a subject. Apparently some speakers who do not understand the grammar of who/whom have the idea that whom is just a more elegant way of saying who.
Bottomline: If you don’t understand the mechanics of whom, don’t use the word at all.
