Mozart, Brahms and their ilk wrote genius, timeless works, but they are not the be-all end-all of classical music that did not go out of fashion with the muttonchop sideburn. In the 20th century, along with explosions in technology, came explosions of nuclear weapons and wars of unprecedented destruction that influenced music to an astounding degree. The classical music to which we most often listen only touches on dissonant intervals-think those famous chords in Beethoven's "Eroica" symphony. The 20th century's explorations brought more dramatic dissonance to classical music.Ralph Vaughan Williams' A Pastoral Symphony, unlike Beethoven's "Pastoral" sixth symphony, goes beyond aurally describing the misty beauty of the British countryside. Strange intervals and a wordlessly keening female soprano recall Vaughan Williams' experiences in World War I, at once gorgeous, tortured and sad. Krzysztof Penderecki went further, ignoring all musical rules to evoke large-scale demise in his threnody to the Victims of Hiroshima.

The 52 strings play ear-warping tone clusters until listening is as painful as contemplating the horror of the assault on Hiroshima. Similarly, Arnold Schinberg's A Survivor from Warsaw uses a male narrator and chorus accompanied by orchestra to literally tell the story of a trainful of Jewish men spontaneously singing the "Sh'ma" prayer as they travel to the death camps. The piece is difficult to listen to because of the discord, and grows in its intensity when the desperate cries of the narrator and the swan song of the doomed chorus come into play.

But the use of dissonance in 20th- century classical music goes beyond pain and suffering. The return to nature as a muse brought out a new and unexplored facet of disharmony that requires the listener to hear beyond the aural pain of a tone cluster. Beyond Stravinsky's Rite of Spring is Tan Dun's Ghost Opera, which blends traditional Chinese instruments and harmonies (themselves often discordant to the Western ear) with atypical scales and "instruments" like bowls of water and rocks. The work is sometimes humorous, often bizarre and always interesting. And Toru Takemitsu, one of Dun's mentors, took back what Impressionists like Ravel and Debussy had stolen and brought Western aleatory, or "chance music," to works like A Flock Descends Into the Pentagonal Garden, a daringly complex and vivid depiction of birds in motion.

If the extreme dissonance of A Survivor from Warsaw or the outre instrumentation of Ghost Opera render these pieces unlistenable, much of the range and versatility in dissonance can be explored in just three pieces, all of which are easier on the ear: La Cathédrale Engloutie by Debussy, the Trio No. 2 of Dmitri Shostakovich and Schinberg's Transfigured Night. The first is an underwater exploration of a sunken cathedral; every enigmatic chord is replete with imagery, and the mystery is enhanced by discordant intervals. Shostakovich's trio is a perfectly brilliant emotional outpouring that intimates through dissonance the composer's pain at the death of a close friend and the ravaging of his native Russia by war and the Stalinist regime. And Transfigured Night is an adolescent flirtation with atonality that adapts to music poet Richard Dehmel's tale of a dark love story of a man and a woman taking a moonlit walk through a forest. Just as one can learn about beauty from Debussy's dissonance or about loss from Shostakovich, Schinberg uses disharmony to describe the pitfalls of love. In short, personal interpretation and contemplation can take us beyond the aural discomfort of a tritone or tone cluster into an entirely new realm of 20th-century expression.