The art of music never enjoyed (or suffered) a link to the tangible world that was comparable to representation in painting, or to the reference of words in literature. But it did have its own stable, generally accepted set of principles, its own traditional internal logic. This rested upon elements that we have discussed many times in this book: tune, motive, harmony, tonality, tone color, and rhythm.

The music of Bach, Beethoven, and Brahms was based on this logic, and so was the entire stream of Western European folk songs, popular songs, dances, military marches, and the rest. Avant-garde modernist music moved away from this norm. Like abstract, nonrepresentational painting, this music worked out new principles based on the materials of the art itself.

With European music before World War I, we can lay special emphasis on developments in melody, harmony, and tonality, for on the whole, these features were the main preoccupations of avant-garde composers in that period. Developments in tone color and rhythm — or, more broadly, musical sonority and musical time — dominated a later stage of avant-garde music, after World War II.