Look at the classical music charts these days, and you aren’t likely to find Bach. Crossover rules now. “It’s easy to see all this as merely a matter of marketing or cynical exploitation. But there seems to be something deeper involved, a breaking down of barriers that has classical musicians moving into what used to be pop territory and pop musicians nibbling around the edges of the classical pie. The world of music is changing, and the result may be something the Three Bs would hardly recognize.”