Question of the Day: Is a Hamburger a Sandwich?

I was at a graduation party for my brother, and had a huge discussion that engulfed all of those in attendance. The questions was whether a hamburger was considered a sandwich?

I answered no, saying that in restaurants, burgers are there own category, they are never listed under sandwich's and when you order a burger, you don't call it a 'burger-sandwich.'

Others said that it was seeing as it was a protein in-between two-pieces or bread, but are buns considered bread or are they there own category as well?

This went on for a while and no conclusions were drawn. So, what do you all think?