@The Pentacle Queen,
I'll add one more work to the list of quintessentially postmodern music: Terry Riley's In C
. Though it is sometimes described as a conservative retreat from the progressive "avant-garde" works coming out of Darmstadt and Princeton, In C
(along with the style it helped to create, minimalism) actually represents the first genuine avant-garde in 20th century classical music. Unlike Boulez and Babbitt, the minimalist composers actually came from outside the institution (meaning their musical style was not sanctioned by academia). This is one of most frequently (and, I think, deliberately) overlooked aspects of the Darmstadt and Princeton schools: for all that its composers presented themselves as progressively avant-garde, by the 1960s they represented the dominant paradigm of classical music, which ironically meant they now represented the conservative old-guard. The best illustration of this is in all the whining Boulez and Babbitt did in an effort to make their music seem as confrontational and anti-establishment as possible. The moment they began to care about their status as avant-garde artists, Boulez and Babbitt ceased to be avant-garde.
Similar to Berio, the minimalists are also among the first generation of composers for whom recordings were the primary method of musical dissemination, making them distinctly different from the composers of the past. This shows not only in their heavy use of recording technology in their pieces but in the general eclecticism of their styles: minimalists jump quite comfortably from classical idioms to pop idioms to non-Western idioms and back again. All of these styles were available to them in equal measure through recordings and, as a result, gave them a synchronic view of musical history altogether different from the linear, "evolutionary" model that their predecessors had inherited.
violates all sorts of modernist taboos, beginning with the sanctity of the artwork. If you've seen the score
then you know that many basic details are not specified, such as the instrumentation, number of players, dynamics, tempo, or even the duration of the piece. The work can last five minutes or five hours, played by two musicians or an entire symphony orchestra. Every performance of the piece is different owing to the personal decisions that the performers are allowed to make.