The following is an extract from New Yorker music critic Alex Ross’s new book The Rest Is Noise, a guide to twentieth century classical music. It provides some insight into the differences between Sibelius and Mahler, and their approach to symphonic composition.

In 1904, Sibelius tried to escape the embarrassments of his Helsinki life style by moving with his wife and three daughters to Ainola. There he set to work on his Third Symphony, which was itself a kind of musical escape. In contrast to the muscular rhetoric of “Kullervo” and the first two symphonies, the Third speaks in a self-consciously clear, pure language. At the same time, it is a sustained deconstruction of symphonic form. The last movement begins as a quicksilver Scherzo, but it gradually, almost imperceptibly, evolves into a marchlike Finale: the listener may have the feeling of the ground shifting underfoot.

Shortly after finishing this terse, elusive work, Sibelius got into a debate with Gustav Mahler on the nature of symphonic form. Mahler went to Helsinki in 1907 to conduct some concerts, and Sibelius presented his latest ideas about “severity of form” and the “profound logic” that should connect symphonic themes. “No!” Mahler replied. “The symphony must be like the world. It must be all-embracing.”
From The Rest Is Noise, Chapter 5: Apparition from the Woods: The Loneliness of Jean Sibelius

It’s also worth reading the following extract for background on Mahler, from the first chapter of the book, The Golden Age: Mahler, Strauss, and the Fin de Siècle. You can read regular postings from Alex Ross on his excellent blog of the same name: The Rest Is Noise.