The way I see it, anything between two other pieces of another thing (separate pieces or conjoined, doesn't matter) constitutes a sandwich. If we accept the ori

The way I see it, anything between two other pieces of another thing (separate pieces or conjoined, doesn't matter) constitutes a sandwich. If we accept the origin story (urban legend?) of its origin as invented by the Earl of Sandwich so that he and his friends can snack without getting their hands dirty during card games, then the sandwich can't be defined as a specific food item, but by the act of putting one thing between two others. Furniture is anything used to "furnish" a space. If the shelf was attached to the wall after the wall is built, it's furniture. If it was built as part of the wall, it isn't.