This is a chapter from Alex Ross's groundbreaking history of twentieth-century classical music, 'The Rest is Noise'. Further extracts are available as digital shorts, accompanying the London Southbank festival programme. Profiling Debussy and Schoenberg, two of the century's earliest innovators, Ross traces the development of atonality, and with it the reinvention of Western harmonic tradition. Now a major festival running throughout 2013 at London's Southbank, The Rest is Noise is an intricate commentary not just on the sounds that defined the century, but on art's troublesome dance with politics, social and cultural change. Alex Ross is the New Yorker's music critic, and the winner of the Guardian First Book Award and the National Book Critics Circle Award for The Rest is Noise, which was also shortlisted for the Samuel Johnson and Pulitzer prizes for non-fiction.