Augmented 6th Chords – Italian 6th

Augmented sixth chords are altered chords that contain the interval of an augmented sixth.

There are various versions and uses of augmented sixth chords. To understand what they are and how they function, let’s look at some examples.

In this lesson, the Italian augmented sixth chord is introduced.

Mozart’s Piano Sonata No. 6, K. 284, Mvt. 3, Variation VII

Let’s look at Movement 3, Theme and variations, of Mozart’s Piano Sonata No. 6 in D major, K. 284, which was written in 1775. We will concentrate on Variation VII, which is in d minor. The entire variation is shown below with a link to an performance of the variation.

Mozart Piano Sonata No. 6, Mvt. 3, Variation VII, mm. 1-8

The variation is in Rounded Binary form. We will look at the A section (mm. 1-8) which starts in D minor and modulates to the key of A minor in measure 5. The example below shows most of the A section analyzed with the exception of two chords, one in m. 3 and one in m.6 (marked in purple). We will discuss the first chord (m. 3) in this lesson.

Italian 6th chord (m. 3)

The chord on beat 4 of measure 3, Bb-D-G#, can be seen below.

Although the chords looks a bit strange, its sound is something we have heard below. Listen to the chord.

As you can hear, this chord sounds like an incomplete dominant 7th chord built on Bb, a Bb7 chord, since the G# (top note) is enharmonic to Ab.

However, this chord does not behave as a dominant 7th chord. If this chord functioned as a dominant, this Bb7 should resolve to an Eb chord as shown below.

Instead, this chord resolves to a cadential 64 to V in the key of D minor.

Both the Bb and the G# (the interval of an augmented 6th) of this chord (the first chord above) resolve outward to the A, the dominant of the key of D. Thus the chord is really pulling to the dominant, in this case via the cadential 64.

We call this chord an Augmented 6th chord because it contains the interval of the augmented 6th. This is a typical augmented 6th chord as its bass is the note a half-step above dominant and the chord resolves to the dominant; the interval of the augmented 6th expands to the dominant in the key (scale degree 5).

This particular augmented 6th chord is an Italian 6th. It contains three notes: The bass (which is a half-step above the dominant), the note an augmented 6th above the bass (the note a half-step below dominant), and a major 3rd above the bass.

So in our analysis of the Mozart Variation, we mark this chord as an Italian 6 or It6.

We still have not tackled the chord in measure 6. That chord will be analyzed in the next lesson (German 6).

Jazz notation for the Italian 6

Since the Italian 6 chord is enharmonic to an incomplete V7 chord, in jazz notation this chord is marked as a dominant 7 chord.

The example below shows the Mozart Variation analyzed with both roman numeral analysis and jazz chords.

Summary

So far we have learned about the Italian 6th chord.

Augmented sixth chords are altered chords that contain the interval of an augmented sixth.

The most common augmented sixth chords are based on the note a half-step above the dominant. All augmented 6th chords also contain the note a half-step below the dominant – creating the interval of the augmented 6th.

The Italian 6th chord also contains the intervals of a Major 3 and augmented 6. This chord will sound like an incomplete V7 chord.

The interval of the augmented 6th usually resolves out to an octave. These chords will resolve to the V or V7 chord (or a cadential 64 chord).

In jazz notation, the Italian chord is marked as dominant 7 chords.