When should you use who, and when should you use whom?
These days, it is becoming rare to see whom, because most of us use who in almost all cases. In fact, whom can sound rather pretentious and stuffy, For example:
To whom am I speaking?
Whom am I speaking to?
These sound very formal. Many of us would be more inclined to write or say:
Who am I speaking to?
Nonetheless, there are still a few stock phrases that use whom, even in contemporary English. For example:
To whom it may concern
In almost all other cases, it has become acceptable in contemporary English usage to use who.