Classical music as most of us think of it—say, from 1575 to 1950, from Monteverdi to Bach to Stravinsky, Rachmaninoff, and so on—has diverged into two streams. Some of the best music in that tradition is now being written for films by composers such as John Williams and Jerry Goldsmith, but—lamentably—it is only infrequently the object of directed listening, as in a concert hall. The second stream (often written by contemporary composers in music conservatories and universities) is twentieth-century (now twenty-first-century) art music, much of it challenging and difficult for the average listener because it pushes the boundaries of tonality, or in many cases is atonal.