Augmented Sixth Chords

An augmented sixth characterizes an important group of dominant preparation chords. The augmented sixth arises out of both mixture and chromaticism: most characteristically, the augmented sixth occurs between the lowered sixth degree of the scale and raised scale degree four. The resulting interval, an augmented sixth, resolves in contrary motion by half step--that is--it expands to an octave built on scale degree five.

There are three main types of augmented sixth chords:

  1. The Italian (augmented 6th plus a 3rd above the bass--scale degree 1) moves directly to V. Double third above bass, as it is the most stable element of the chord.

  2. The German (Italian sixth plus a perfect fifth above the bass) This chord almost always proceeds to a V, to avoid parallel fifths. The German augmented sixth chord is the only augmented sixth chord that is enharmonic with a dominant seventh chord.

  3. The French (Italian sixth plus an augmented fourth above the bass scale degree 2) moves directly to V.

As with most of the chords that we know, the function of a particular chord hinges on the melodic tendencies of the bass voice and its position within a key.

Because the majority of augmented sixth chords are built upon the lowered sixth degree in major, they often function as a chromatically altered II or IV chord. VI is another important harmony that may precede an augmented 6th chord.

Three voice-leading possibilities are most common:

  1. A "chromaticized" voice exchange between soprano and bass.
  2. The chromatic inflection of scale degree 4 (soprano).
  3. The chromatic inflection of scale degree 6 (bass).

Other possibilities include:

  1. (in C minor) A French sixth resolves to V7 (irregular resolution of the augmented 6th).
  2. (in A major) Chromatic expansion of I. (Chromatic expansion of V also possible).
  3. (in C major) Passage from I6-I.

Augmented 6th chords sometimes play an important role in effecting large-scale modulations by affirming the new key's dominant. Consider the following figured-bass plan.

Compare this plan with pp. 271-272 of your Burkhart anthology.

In other instances, a motivic impulse might lead a composer to utilize an augmented sixth chord. See Schumann, Vogel als Prophete (from Waldscenen, Op. 82) in your Burkhart anthology, pp. 321-323 (mm. 24-25).

Inversions of augmented 6th chords

  1. Chopin, Op. 28, No. 22 (Listen for raised 4 [fi] in the bass).
  2. Brahms, Op. 76, No. 4 (scale degree 1 becomes 3rd of g-minor).

Created 10.25.99