When patriotic country music fans sing Lee Greenwood's lyric ''I'm proud to be an American, where at least I know I'm free,'' what do they mean? Is Greenwood's idea of freedom the same as Bruce Springsteen's or Francis Scott Key's? And is this freedom the same as the liberty of the Declaration of Independence, the Pledge of Allegiance or the statue in New York Harbor? In ''Liberty and Freedom,'' David Hackett Fischer, a historian at Brandeis University, argues that we cannot learn how most Americans understand freedom by studying political theory or intellectual debates. ''Most Americans do not think of...