In graduate school, at least in the sciences, we refer to all the professors by their first name. I think it's just better for everyone to address their undergraduate professors as either doctor or professor. If someone calls me by my first name, I'm not going to complain. It's not a big deal. There are more important issues out there to worry about. Eric Dovigee says, the possibility of unperceived existence is weird; can this exist? Gary Upshaw: Can something that exists but isn't labeled as such be called "nothing?"