And the cultural pressure has gone farther than this. Not only has the increasing complexity of life broadened the musician's personal outlook, professional or unprofessional: it has also modified, whether for better or for worse, the outlook of the music itself. We may conveniently divide all music into two great classes: 'absolute' music, in which the composer appeals to the listener through the direct medium of the pure sound and that alone; and 'applied' music, in which the appeal is more or less conditioned by words, either explicit or implicit by association, or by bodily movement of some kind, dramatic or not, or by any other non-musical factor that affects the nature of the composer's thought and the method of its presentation. Up to the present generation, instrumental music, unconnected with the stage, has been virtually identifiable with absolute music; there are a handful of exceptions--sporadic pieces, usually though not invariably thrown off in composers' relatively easy-going moods, and an isolated figure or two of serious revolt, like Berlioz and Liszt--but they only serve to prove the rule. Now, this identification is far from holding good. More consciously than ever before, instrumental music is straining beyond its own special domain and asking for external spurs to creative activity. And it asks in various quarters. It may ask merely the hint of particular emotional moods conditioned by special circumstances; or it may vie with the poet and the novelist in analysis of character. The psychology, again, may pass into the illustration of incident, whether partially realistic or purely imaginative, or into the illustration of philosophical tenets, as in Strauss's version of Nietzsche's doctrines in his _Also sprach Zarathustra_ or Scriabin's of theosophy in his _Prometheus_. Or the composer may go directly to painting, whether actual as in Rachmaninoff's symphonic poem on Böcklin's picture of 'The island of the dead', or visionary as in Debussy's 'La cathédrale engloutie'. There is indeed no end to such instances.
All this development of instrumental music into territories more or less adjacent makes a very imposing show; and it is so markedly a product of the last generation that we easily over-estimate the novelty of its essential results. As I have said, instrumental music is more and more asking for external spurs to creative activity; but this does not mean that music as a whole is, so to speak, breaking loose from its moorings and adventurously voyaging on to uncharted seas. What it means is, simply, that, under the stress of modern culture, the barriers between vocal and instrumental, dramatic and non-dramatic, music have been to a great extent abolished.