In one of my theory classes as an undergrad, my comp teacher noted that the prevalent interval classes had, for the most part, evolved along the path of the overtone series: chant (octaves), organum (fifths), common practice (thirds) early 20th century (seconds) later 20th century (microtones). So what was next, he asked with a smile.
I thought unison would be a dreadfully boring place to go, but then, Reich and Andriessen were doing things with imitation at the unison that was pretty exciting. There was also the idea of heterophony. While very common in non-western music, and even some western folk traditions, heterophony is only touched on occasionally by modern composers, and more as a decorative orchestration technique than a substantive idea in a piece.
One of my first successes with a more formal approach to heterophony is a movement from Taxonomy for flute and clarinet. The movement, Elaphe, evokes the genus of snakes it is named for by presenting patterns then blurring them (the main, if pitiful, defense ratsnakes have against predators). A pattern is presented in the clarinet, and the flute grabs on to certain notes, making it seem that the clarinet has left ghosts, or echoes, or is anticipated. While a bit more complex than doubling the melody with some ornamentation, it has a similar “thickening” effect that heterophony does in the music of Ireland or Thailand. One difference, however, is that in traditional heterophony the rhythmic edges are softened, whereas in this style they become more angular.
Betsy Bobenhouse, Flute; Christy Banks, clarinet.