Someone recently sent me an email asking about the proper use of who and that:
When followed by a verb, how does one know when to say “who” and when to say “that”? Ex: The lady that jumped on the couch or The lady who jumped on the couch?
I prefer to use who when referring to people, but that is merely a preference. My favorite online source for such usage questions, The American Heritage Book of English Usage, explains:
that instead of who
The man that wanted to talk to you just called back. Some people say that you can only use who and not that to introduce a restrictive relative clause that identifies a person. But that has been used in this way for centuries. It is a quintessential English usage, going back to the Old English period, and has been used by our best writers. So it is entirely acceptable to write either the man that wanted to talk to you or the man who wanted to talk to you.
You can read more about such pronoun issues in The American Heritage Book of English Usage at bartleby.com