While every chord we have studied in the course thus far has been based in tertian harmony, the chords that we will explore do not rely on intervals of the third for their construction. Although they are no more difficult to understand functionally. Interestingly, this chord type comes in three different variants. (You can think of them as “flavors” if you’d like.)
Analyze and listen to the following short progressions. There are two progressions – one in major, one in the parallel minor – for each of the three variants of this unusual chord. Start your analysis with leadsheet symbols and then provide Roman numerals when possible. In each progression, study the chromatic chord to answer the following questions:
The augmented sixth chords are collections of pitches that create smooth voice-leading. They function based on their voice-leading only, not tertian harmony, so it is unhelpful to describe them using standard chord terms such as root, third, and fifth. Instead, we typically describe the chordal members by their scale degrees. In the table below, you can see that all augmented sixth chords share three common tones – ^b6, ^1, and ^#4. As you hopefully determined from the first examples, the Italian variant consists of only the three primary pitches whereas the German and French variations have an added tone. (For ease of communication, I will always refer to the lowered sixth scale degree as ^b6 even though it is already lowered by the key signature in minor. This goes the same for the ^b3 in German augmented sixth chords.)
| +6 variant | Chordal member | Chordal member | Chordal member | Chordal member |
|---|---|---|---|---|
| Italian | ^b6 | ^#4 | ^1 | ^1 (doubled) |
| German | ^b6 | ^#4 | ^1 | ^b3 |
| French | ^b6 | ^#4 | ^1 | ^2 |
Augmented sixth chords are named because of the augmented sixth interval that is created between the ^b6 and ^#4. This interval also creates the defining voice-leading feature for this chord. Look at the following examples. How does the augmented sixth resolve? How does it change if it is inverted? Does resolving the tendency tones in any of the chords present voice-leading issues.
As you can see, the tendency tones of the augmented sixth–^b6 and ^#4–will always resolve by a half-step. If the ^b6 is in a lower voice than the ^#4, they will resolve outward by half-step to an octave. If the ^#4 is in a lower voice than the ^b6, they will resolve inward by half-step to create an octave. The resolution of this interval is the entire reason for the existence of these augmented sixth chords, so you can consider this resolution of the defining characteristic of these chords.
There are certainly voice-leading issues when resolving augmented sixth chords, but the chromatic element, particularly the ^#4, somewhat camouflages the objectionable parallels. Most obviously, when a Ger+6 resolves directly to a V chord, parallel perfect fifths will result when resolving the ^b6 and ^b3 scale degrees. For this reason, there are alternate resolutions for augmented sixth chords that are often preferable. Look at the next example to see two possible fixes for this. Does the cadential I6/4 fix the likely objectionable parallels for a Ger+6? Why does the Ger+6 have an enharmonically spelled pitch when resolving to a cadential I6/4? When an augmented sixth chord resolves to a V7, what changes about the resolution of the tendency tones in the augmented sixth chord?
Passing through another chord can hide the objectionable parallels created by the tendency tones of the Ger+6. In particular, a cadential 6/4 chord can still provide the standard resolutions for the tendency tone (to the dominant scale degree) but also provides an outlet for the ^b3 to resolve by half-step to the third of the I6/4 as you can see in the first example. In this case, the ^b3 will often be re-spelled to a ^#2, but this does not change the function or labeling of the chord.
The other option that is commonly used is resolving any augmented sixth chord to a V7 chord rather than a triad. In this case though, the smoothest resolution to the seventh of the V7 is to alter the resolution of one of the tones that create the augmented sixth interval–particularly, the ^#4. Instead of resolving upward by half-step to sol, you can resolve the ^#4 downward by half-step to the seventh of the V7 as demonstrated in the second example above.
As you probably noticed in the examples above, there is no change in the inversion figure for any of the augmented sixth chords. Because these are not based in tertian harmony, there is no standard inversion figure that would explain the intervals. Therefore, rather than create an entirely new set of inversion figures for one uncommon chord, we simply notate each of these chords with the same “Roman numeral” symbol, regardless of inversion. They are:
| +6 variant | Analysis symbol |
|---|---|
| Italian | It+6 |
| German | Ger+6 |
| French | Fr+6 |
In all of the examples thus far, the interval between the ^b6 and ^#4 – augmented sixth – has resolved outward to emphasize a specific scale degree, ^5 or sol. Because of this, we assume that a standard augmented sixth chord has a predominant function, because it emphasizes the root of the dominant. As with any colorful chord, however, composers do not restrict themselves to this one usage. Analyze the following example. How would you describe what is happening in the penultimate chord?
The penultimate chord does not function as tertian harmony, and it clearly resolves as an augmented sixth chord. The D-flat and B-natural form an augmented sixth that resolves outward by half-step, and the two inner voices create a German+6…in a different key.
These non-dominant resolutions present an issue for standard Roman numeral notation. Before reading on, take a moment and try to come up with a label for the the augmented sixth chord in the previous example. The standard German augmented sixth in that key (C major) would have an A-flat, C, E-flat, and F-sharp, so you cannot simply label it as Ger+6.
Augmented sixth chords are similar to secondary dominant functions in that they embellish a chord using chromatic alterations that strengthen voice leading. A tonicization, however, temporarily treats a non-tonic chord as if it were tonic. Our notation for secondary dominants shows this by using a slash to imply that we are temporarily working in the key of the chord below the slash. In the example above, the augmented sixth chord is the standard Ger+6 in the key of F major, so some theory methods suggest that you should use a slash to label this as Ger+6/IV, because this chord would appear in the key of F major. I find this inadequate because in the key of F major, this chord would function as a pre-dominant harmony whereas it is clearly filling a dominant function here. Other theory methods recommend that this chord be labeled as Ger+6/I to show that it is meant to resolve to the I chord, but this fundamentally alters what the slash means. A slash chord above a Roman numeral means “in the key of”; V/V implies a V chord in the key of the dominant. Using Ger+6/I would mean the Ger+6 in the key of I–in this case, C major–but the standard Ger+6 in the key of C major has A-flat, C, E-flat, and F-sharp.
Instead, the least ambiguous option for alternate resolutions of augmented sixth chords is to show what pitch the chord is intended to embellish by placing a scale degree below a slash. Therefore, the example above would be labeled as Ger+6/^1. Using a scale degree below the slash instead of a Roman numeral makes it clear that the slash is functioning differently than its use in labeling secondary functions.
Because augmented sixth chords are based entirely on the smooth voice leading that they create, you could use an augmented sixth chord to embellish almost any harmony, although it does work best for major triads and dominant chords. Try this for yourself in the following progression by inserting augmented sixth chords at any spot marked with an x. You may change any note necessary for the chord. Please note that each chord will need a “customized” augmented sixth chord that emphasizes its root; there is no one-size-fits-all augmented sixth chord. For example, if you plan to use Ger+6/ii, you would need to make sure that you are using an augmented sixth chord that has an augmented sixth that resolves outward by half-step to ^2.