Augmented Sixth Chord
A chromatic predominant chord built on the augmented sixth and resolving to the dominant
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An augmented sixth chord is built around the augmented sixth between the lowered sixth degree and the raised fourth, the two voices expanding outward to the octave on the dominant. Three forms are common: the Italian sixth (♭6–1–♯4), the French sixth (adding 2) and the German sixth (adding ♭3).
All three are chromatic predominants, normally leading to the dominant or a six-four. The German sixth sounds like a dominant seventh, but its bass is ♭6, not 5, and it functions as subdominant preparation; resolving it directly can produce parallel fifths, so a six-four is often used.
The "sixth" in the name is an interval, not the first inversion of a triad, and the three types are not chords on different roots but variants of one framework. Enharmonic respelling can change the notation and destination while sounding the same.
Sources
- 三种类型、构造与解决参 The New Grove Dictionary of Music and Musicians, "Augmented sixth chord"；本文为原创表述
Used for fact-checking only; all prose is original.