Music Since the Twentieth Century
Time for another music history lesson.
By the turn of the century, late Romanticism was beginning to die out. Gustav Mahler was writing symphonies of epic proportions, Maurice Ravel and Claude Debussy were defining a musical style dubbed "Impressionism" - though Debussy hated the term - and Alexander Scriabin was writing increasingly mystical music based on his own egomaniacal philosophy. These folks, and figures like them, were continuously evolving the musical language that had existed more or less continuously from about 1600, when the Baroque era started. Romanticism was fracturing, and there were sub-groups of composers who sought their own styles, and composers who simply struck out on their own path.
As time went by, harmony was extended, and by 1900 the usage of chromatic harmony - a technique whereby harmonies are derived from both pitches within the scale of the music you're working in and from without - was everywhere. In many composer's eyes, these kinds of rich, expanded tonal structures would go on indefinitely, with composers adding to the additions that had been accrued over the years.
Other composers thought that there simply was no place to go, that traditional tonality had reached its breaking point, and new rules had to be developed. Scriabin, who started out writing very Chopinesque music, evolved his own brand of harmony derived from fourths, altered dominant chords, and a few stunning examples of bitonality in some of his late preludes. Igor Stravinsky embraced rhythmic drive (and bitonality as well) in The Rite of Spring, which was so groundbreaking that the first performance was marred by a riot in the Parisian audience.
Most lasting was the music of the so-called Second Viennese School, headed up by Arnold Schoenberg. Schoenberg's first few opuses show the influence of Mahler and is filled with intense chromaticism - so intense that even those early works - far and away his most accessible pieces - were met with incomprehension at their first performances. Undaunted, Schoenberg veered into extreme atonality, writing pieces such as Pierrot Lunaire. Pierrot made waves not just with its atonality, but for its unique ensemble (known henceforth as the Pierrot Ensemble) and with its half-speaking, half-singing writing for voice.
But Schoenberg, for all of his cacophonous music, realized that this kind of free dissonance and atonality - something that composers such as Charles Ives and Leo Ornstein had experimented with - needed some sort of structure to hold it together, just as tonality had held music together before him. To make a long, diagram-necessitating story short, he came up with something called the 12-tone technique, whereby every note was sounded equally through the use of tone rows, which were essentially randomized chromatic scales.
Schoenberg's two major pupils, Anton Webern and Alban Berg, took Schoenberg's techniques and personalized them. Webern idolized Schoenberg and often moved just so he could be near him, and took the 12-tone technique and honed it to a disjointed science. Webern was known for writing exceptionally short pieces, and his piano music is characterized by its brevity, sparseness, and unholy dissonance. He died at the end of World War II after a trigger-happy American soldier saw his cigar and mistook him for an enemy soldier ... but strange composer deaths are a story for another time.
Despite the fact that his music was aesthetically terrible, Webern became one of the most important modern composers, for the avant-garde for most of the rest of the century followed his lead to some extent. The 12-tone technique was applied to other areas of music - instruments, dynamics, note lengths - to derive an incredibly strict kind of "total serialism," where the composer writes a few rows and the music more or less writes itself.
Alban Berg, on the other hand, experimented with making Schoenberg's ideas accessible. He wrote a masterpiece of a Violin Concerto and an opera, Wozzeck, which half-succeeded in this endeavor. He's considered the easiest atonal composer to listen to. His middle-ground approach makes him an oddball figure on both sides of the fence.
But back to Webern, whose techniques had a significant impact. Pierre Boulez took Webern's usage of serial composition to every extreme imaginable, writing music where every imaginable aspect is controlled by rows - pitch, velocity, register, etc. While Boulez has always composed this kind of music, even he realized that total serialization leaves no room for creativity.
The Greek composer Iannis Xenakis took off in a different direction. A mathematician and an architect, Xenakis was one of the first composers who took to "Musique Concrete" techniques - sound collages of recorded tape. Aside from his solo percussion pieces, his music is frankly ridiculous, as he wrote music based on mathematical formulas. Similar approaches were taken by Karlheinz Stockhausen, a controversial and influential figure in the sphere of electronic music, and who once wrote a string quartet where every instrument is lifted on a separate helicopter.
I give all these examples to illustrate one point: since Schoenberg, many composers have taken refuge in music that is of theoretical interest, but not traditional musical interest. Say what you want about Schoenberg, Webern, Boulez, and Xenakis, but their music is aesthetically unpleasing. They thought that there was nothing of strict musical interest left to say, and so they found their own paths.
These paths are now showing themselves to be dead ends. The same strict adherence to predefined sets of rules makes much "modern" music as boring and as aesthetically similar to music of the Classical era.
But it's not like all 20th-century composers took to serialism. Alfred Schnittke and György Ligeti were remarkably innovative and wrote significant pieces without adhering to the strict serialism that had gripped much of the classical music cognoscenti. Schnittke likened his departure as getting off an overcrowded train, and Ligeti mercilessly parodied his fellow composers in his Poème Symphonique for 100 metronomes.
Other composers, such as Henryk Górecki, Lowell Liebermann, Einojuhani Rautavaara, and John Corigliano have abandoned serialism in favor of a return to late Romanticism, a kind of musical reboot. They all have written music of musical and theoretical interest. Even Krzysztof Penderecki, a noted avant-garde composer who gained fame through his manic pieces for string orchestra (Threnody for the Victims of Hiroshima and Polymorphia among them), abandoned that style, saying that we "must go back to Mahler and start over."
Suffice it to say that I very much agree with Penderecki.