Editing Quartal and quintal harmony (section)

==== Schoenberg ====
[[Arnold Schoenberg]]'s [[Chamber Symphony No. 1|Chamber Symphony Op. 9]] (1906) displays quartal harmony: the first measure and a half construct a five-part fourth chord with the notes (highlighted in red in the illustration) A–D{{music|sharp}}–F–B{{music|flat}}–E{{music|flat}}–A{{music|flat}} distributed over the five stringed instruments (the viola must tune down the lowest string by a minor third, and read in the unfamiliar tenor clef).

[[File:SchoenbergOp9.png|thumb|center|upright=1.4|Vertical quartal-harmony in the string parts of the opening measures of Arnold Schoenberg's Chamber Symphony Op. 9[[File:SchoenbergOp9.mid]]]]

[[File:Schönberg Kammersymhonie 9 for wikipedia.png|thumb|upright=1.25|Six-note horizontal fourth chord in Arnold Schoenberg's Chamber Symphony Op. 9|alt=]]

The composer then picks out this vertical quartal harmony in a horizontal sequence of fourths from the horns, eventually leading to a passage of triadic quartal harmony (i.e., chords of three notes, each layer a fourth apart).{{citation needed|date=September 2012}}

Schoenberg was also one of the first to write on the theoretical consequences of this harmonic innovation. In his ''Theory of Harmony'' (''Harmonielehre'') of 1911, he wrote:
{{quote|The construction of chords by superimposing fourths can lead to a chord that contains all the twelve notes of the [[chromatic scale]]; hence, such construction does manifest a possibility for dealing systematically with those harmonic phenomena that already exist in the works of some of us: seven, eight, nine, ten, eleven, and twelve-part chords… But the quartal construction makes possible, as I said, accommodation of all phenomena of harmony.{{sfn|Schoenberg|1978|loc=406–407}}}}

For [[Anton Webern]], the importance of quartal harmony lay in the possibility of building new sounds. After hearing Schoenberg's Chamber Symphony, Webern wrote "You must write something like that, too!"{{sfn|Webern|1963|loc=48}}