What is an Italian Augmented Sixth?

An Italian augmented sixth chord (often called the Italian sixth or It+6) is a type of augmented sixth chord used in tonal harmony to create strong tension that resolves to the dominant chord. It is named after Italian composers who frequently used this harmonic structure during the Baroque and Classical periods.

The Italian augmented sixth chord typically contains three notes: the lowered sixth scale degree (♭6), the tonic (1), and the raised fourth scale degree (#4). The key feature of the chord is the interval of an augmented sixth between the ♭6 and #4. These two notes resolve outward by step to the dominant note (5), creating a strong pull toward the dominant chord.

For example, in the key of C major, the Italian augmented sixth chord would contain the notes A♭ (♭6), C (1), and F♯ (#4). The A♭ and F♯ form the augmented sixth interval and resolve outward to G, the dominant of the key. Because of this strong motion, the Italian sixth is commonly used just before the dominant chord to intensify the harmonic progression.