Audio: quartal harmony (0:08)
quartal harmony plays tertian and quartal harmony on the piano. Two identical harmonies are played in sequence. The first, in the key of D minor, is notated in tertian harmony, and the second, in the parallel key of D major, is notated in quartal harmony. The quartal harmony figure shows the score.
Quartal harmony is based on an interval of a fourth.
A quartal chord is not a tertian chord. It is constructed using the interval of a fourth whereas a tertian chord is constructed using the interval of a third. A quartal chord is not a triad. A triad has three notes and is constructed from successive intervals of a third, whereas a quartal chord, which also has three notes, is constructed from successive intervals of a fourth. Quartal harmony is not major or minor harmony. The terms, major and minor, only apply to tertian harmony, not quartal harmony.
A quartal chord can be notated by adding a 4 to the chord name or number, as in bar 6 of quartal harmony. This is not common usage, but it makes sense, and there is no tertian chord with a 4 after its name or number. Thus, the chord D4 is in root position and contains the notes DGC# in the key of D major. Chord notation is based on tertian harmony, so the best that can be done is to try to adapt a quartal chord to tertian notation. Even this can be difficult, and there is no easy way to annotate the DGC chord in bar 2.
A suspended chord can be treated as a modified triad or as an inverted quartal chord. In bar 3, the chord, GCD, is a modified triad and notated Gsus4. Similarly, in bar 4, there is a Csus2. In quartal harmony sus chords are inversions. The GC#D chord in bar 7 is the first inversion of D4. Similarly, C#DG, in bar 8, is the second inversion of D4.
Seven quartal chords can be constructed from the notes in a scale. Five of them contain two consecutive perfect fourths (P4+P4), the remaining two contain a perfect fourth and an augmented fourth (P4+aug4 or aug4+P4). There are always two tritones in quartal harmony, compared with one in tertian harmony. This is shown in bars 6-8, which all contain the tritone, GC#.
Quartal harmony is based on the interval of a fourth. This interval is treated as dissonant in counterpoint and banned. It is also banned between the bass and the upper parts in functional harmony.
The existence of perfect fourth and a tritone in quartal harmony illustrates its dissonant nature. This may account for the fact that the theory and practice of quartal harmony is much less developed than that of counterpoint and functional harmony.
Quartal harmony and quintal harmony are the same. Quartal harmony constructs chords from the intervals of a fourth, quintal harmony constructs chords from the intervals of a fifth. A fourth is the inverse of a fifth. A quartal chord and a quintal chord are two sides of the same coin. Everything that applies to quartal harmony also applies to quintal harmony.
Quartal harmony is not used in functional harmony, which is exclusively tertian. It is occasionally used in pop harmony, although seemingly more by default than design. However, it is a viable approach to harmony and provides an interesting alternative to functional, modal and pentatonic harmony. It also represents the last outpost of the triad, whose passing can be celebrated or mourned, according to taste.