Polychord

Two chords, one sound

A polychord arises when two chords sound at the same time, each with its own root, and the ear can still recognise both. A single chord is built in thirds. Here, by contrast, two complete triads are stacked on top of each other, for example D major over C major. The chord symbol is written like a fraction: the upper chord on top, the lower one beneath. In running text one writes “D over C”. The slash in the symbol D/C means something different on the page Slash chord: there only a single bass note follows the slash.

In the glossary: Triad · Polytonality · Seventh chord

Listening

The first two chords are the building blocks, the third is their stacking. With D over C the lower C major triad sounds firm, the upper brings extra colour with the F♯, which C major does not contain. In the last chord C major and F♯ major lie on top of each other, their roots a tritone apart. That sounds harsher.

The Petrushka chord

The “Petrushka chord” from Igor Stravinsky's ballet “Petrushka” of 1911 is famous. It sounds C major and F♯ major at the same time. The two keys stand opposite each other on the circle of fifths, a tritone apart, and the sound counts as the epitome of simultaneous keys.

In jazz the polychord appears as the so-called upper structure: a chord lies over a bass note or a basic chord and extends it with notes such as ninth, augmented eleventh or thirteenth. The D major above C contains exactly such colour notes for C: D is the ninth, F♯ the augmented eleventh and A the thirteenth.

What a polychord is not

Three neighbouring terms are close but mean something else:

• Slash chord: here only the bass note is changed, for example C/E for C major with E in the bass. It remains a single chord. The polychord, by contrast, consists of two complete chords.
• Polytonality: several keys sound at the same time, also as melody or voice. The polychord stays at the level of the single chord.
• Extended chord: a ninth or thirteenth chord can often also be read as a polychord, and vice versa. It depends on whether you want to hear the sound as one chord with added notes or as two separate chords.