Description
Across all measures of society, the 20th century was a time of huge upheaval, experimentation, and technological innovationand classical music of this period reflected and engaged those societal shifts. Indeed, many of the musical styles and pieces to emerge from even the earliest decades of this century still provoke shock in some quarters nearly a century later, just as some modern visual art continues to divide audiences decades after its creation.
Some of the most fiercely pitched battles (which have continued, in some circles, for several decades) have been between composers who have adhered more closely to traditional diatonic harmony, in which pitches are given a hierarchical priority, and those experimenting with tonal systems that fall outside of that norm. The Second Viennese School, led by Arnold Schoenberg and with his disciples Berg and Webern, pioneered a kind of composition that exhilaratingly freed the language of music; later composers, from Karlheinz Stockhausen and Pierre Boulez in Europe to Milton Babbitt and Elliott Carter in the US, took this new experimentation to even more complex ends. (However, atonality is in many ways the direct descendent of traditional music from the Romantic Era; even in the 19th century and into the very earliest years of the 20th century, greatly beloved composers such as Liszt, Wagner, Debussy, and Richard Strauss were already writing complex and tonally ambiguous works.)
Other 20thcentury composers were writing music that, while perhaps more tonally conservative, were just as engaged in commenting on the world around them. The music of Charles Ives, for example, is the ultimate expression of American democracy, in which the popular tunes of his day jostle shouldertoshoulder with experimental technique; and it is hard to imagine the trajectory of Russian composer Dmitri Shostakovichs output had he not been continually wrestling, both aesthetically and personally, with the dictates and brutalities of Soviet Russia.

