Melody, harmony, and tonality all work closely together. In historical terms, harmony arose as a way of supporting and adorning melody, and tonality first arose as a means of clarifying both melody and harmony; later tonality functioned as a more general way of organizing music. Each of these functions was transformed in the early twentieth century.

The Viennese Classical composers brought tunes to the fore in their music, and the Romantics capitalized on tunes as the most emphatic means of conveying powerful emotion. Yet Wagner, despite the melodic quality of many of his leitmotivs, was criticized for the confusing quality of his singing lines, and Mahler’s audiences were puzzled and irritated by the bittersweet distortions that he applied to folklike tunes. In his later works, his long melodies surge, swoop, and yearn in a strange, almost painful manner.

By that time another Viennese composer, Arnold Schoenberg, was writing even more complex melodies that made little sense to contemporary listeners. The intense rhythms and the anguished intervals of Romanticism were exaggerated almost beyond recognition.

Outside of Vienna, the disintegration of tuneful melody was accomplished in other ways. In many (not all) of his works, Claude Debussy used only the most shadowy motives — a constant suggestion of melody without clear tunes. A little later Igor Stravinsky, writing in Paris, seized upon Russian folk songs but whittled them down into brief, utterly simple fragments — blank, “objective,” and without emotion.