Augmented sixth chord

How Composers Use It

Augmented sixth chords pull hard toward the dominant: the lowered sixth degree in the bass and the raised fourth degree above it form the augmented sixth, which expands by half steps to the octave on the dominant. The Italian sixth has just those two plus the tonic; the French adds the second degree, a dissonant augmented fourth above the bass; the German adds the lowered third degree, a perfect fifth above the bass, so it usually moves through a cadential six-four to avoid parallel fifths.

Example

Chopin's Ballade No. 1 — augmented sixth chords drive the most dramatic harmonic moments, their chromatic intensity propelling the music forward.

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