A true national anthem isn't set by law: it's chosen by the people, often emerges out of conflict, and its meaning shifts over time. All of that and more is true of The Star-Spangled Banner. But still, it was sung by four generations of Americans before it became our official anthem. It's been translated into 40 languages, requires extraordinary athleticism to sing, and has long been both an object of awe and a lightening rod for controversy.

Guest: Mark Clague, author of "O Say Can You Hear? A Cultural Biography of The Star-Spangled Banner" and a professor of musicology at the University of Michigan.