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Twin Sons from Different Mothers: Harmonic Convergence in Jazz and Classical Music, Part 3: "Augmented 6th Chords in Classical And Jazz"

Twin Sons from Different Mothers: Harmonic Convergence in Jazz and Classical Music, Part 3: "Augmented 6th Chords in Classical And Jazz"
...the +6 chord is a tritone sub for the secondary dominant born from linear movement to the dominant. Of course, classical theorists did not use that terminology, but it is the same concept in both styles—remarkably, tritone subs and +6 chords are the same harmonic device.
Part 1 | Part 2 | Part 3 | Part 4

III. Augmented 6th Chords in Classical Music and Jazz

Classical music has its own version of the tritone sub, which, of course, predated the jazz version. It results from the outer voices (usually soprano and bass) moving in contrary motion into the dominant chord, not the tonic, as it so often does in jazz. The interval between the bass and soprano before the dominant is an augmented 6th, which gives the chord its name. There are three kinds of augmented 6th chords—the German augmented 6th, the French augmented 6th and the Italian augmented 6th. The differences between the three types are as follows:

All of them have the two pitches with the +6 between them, the root (A♭) and the +6 (F#). The It+6 doubles the 3rd (C), the Fr+6 has a raised 4th (D) instead of a 5th and the Ger+6 most resembles a dominant 7th chord—it has root, 3rd, 5th (E♭) and +6.

Here is a generic Ger+6 as found in C major, the key to which the second Beethoven example (Symphony #5, Mvt. 2, below) modulates:

The progression introduces two pitches from outside of the key— A♭, the upper leading tone to V, and F#, the leading tone of G (V). The +6 chord thus approaches the dominant from a half-step above and a half-step below:

These sound simultaneously as they move in contrary motion and resolve to G. This splash of color makes the move to the dominant more surprising, which makes the return to the tonic even more satisfying.

Here are a few examples from classical literature:

A Ger+6 occurs at 0:48 in J.S. Bach's Mass in B Minor, "Crucifixus." The chord is usually found in root position, but at 2:49-2:50, we find a Ger+6 in third inversion with the +6 (C#) in the bass—it is such a peculiar sound, an otherworldly effect to approach the final cadence of this haunting passacaglia from one of Bach's most outstanding masterworks.

Beethoven's 5th Symphony, 1st Movement, uses a Ger+6 chord at at 0:16, just before the first pause.

And finally, another Ger+6 chord is found in Franz Schubert's "Die Post" from his song cycle "Winterreise" at 0:21.

The Romantic composer, Richard Wagner used the +6 chord to great effect by featuring it prominently and capitalizing on its unique sound. In Wagner's Prelude to "Tristan und Isolde," the first chord sounded (0:12, then repeated up a minor third at 0:30) is a +6th chord with a non-harmonic tone, the accented appoggiatura on G# that resolves to the third of the chord, A, just briefly at the end of the measure. (This Fr+6 chord with the accented appoggiatura is so famous, in fact, that it gets its own name—the "Tristan Chord.") No key is established, and the piece begins provocatively with the most ambiguous and unstable of the three +6 chords, the Fr+6, with an accented non-harmonic tone no less! All of the +6 chords have tritones in them, but the Fr+6 chord is unique in that it has two tritones in it, one between the 3rd and +6 and another between the root and the raised 4th. This gives it a Lydian flavor that the Ger+6 and the It+6 do not have.

In this example, the Fr+6 does resolve as expected, but Wagner includes an accented passing tone (A#) on the dominant chord which is a tritone from the root; it thus mimics the Lydian (#4) flavor of the Fr+6, creating a particularly poignant and painful longing for resolution.

We can hear that the tonal system is near the end of its reign, as composers like Wagner push tonality to its breaking point. The effect is extremely powerful—hardly anything is more moving, tragic, and evocative than this piece from Wagner. He utilizes what was previously a colorful ornament that cued up the dominant chord. In this instance, however, it was no longer ornamental. The +6 chord, in particular the Fr+6 with the two pairs of tritones that summoned the whole tone scale that the French Impressionists like Maurice Ravel and Claude Debussy would use to such great effect, became a bridge to the music of the 20C.

It is also used in pop music—here we find it in The Beatles "I Want You (She's So Heavy)" where it puts the teeth into the grinding, snarling vamp figure that starts the piece (the +6 first appears at 0:07) and repeats insistently, almost maniacally, for the last three minutes of the tune (4:37-7:47).

The Augmented Sixth as a Tritone Sub?

To see how the +6 functions similarly to a tritone sub, let's revisit our "Body and Soul" example from Part 2:

The +6 in C major is A♭7, with the seventh spelled enharmonically as F# instead of D♭. The +6 in C major is A♭7, with the seventh spelled enharmonically as F# instead of G♭. As we saw in the analysis from Part 2, A♭7 is the dominant of "Body and Soul," but it can be replaced by its tritone sub, D7. This works because the 3rd and 7th of D7 and A♭7 are enharmonically the same pitches, which makes each the tritone sub for the other.

While A♭ is the dominant of D♭, D7 is the dominant of G. As the dominant chord in G, D7 is used regularly as the secondary dominant of the dominant in C major. Here is D7 as a secondary dominant (V7/V) in C major moving to G7 (V7):

Thus, the +6 chord is a tritone sub for the secondary dominant born from linear movement to the dominant. Of course, classical theorists did not use that terminology, but it is the same concept in both styles—remarkably, tritone subs and +6 chords are the same harmonic device.

The difference between these chords in classical and jazz is how they are approached and how they resolve. In classical music, the +6 resolves in dramatic fashion with explosive chromatic contrary motion to the dominant. (There are exceptions to this, but in general, this is how the chord functions in classical music.) The F# notation is thus correct—the pitch resolves as a leading tone does, i.e., upward by half-step to the dominant. In jazz, however, the outer voices resolve in similar motion downward to the tonic. Thus, the G♭ notation is correct—the pitch resolves as a 7th of a dominant chord does, i.e., downward by half-step to the 3rd of the tonic chord.

There is one other striking difference in how they are used in each style. In classical music, composers capitalized on the enharmonic spelling of the 7th in the chord to facilitate surprising modulations to distant keys.

Here is an example of an enharmonic modulation from Beethoven's 5th Symphony, 2nd Movement (piano reduction), from 1808 (excerpt begins at 1:04 in the video and the thunderous Ger+6 chord is heard at 1:10):

Beethoven modulates from A♭ major to C major, a distance of a major third. This movement by major or minor thirds with chromatic inflection is known as a "chromatic mediant," a harmonic device that was quite popular with romantic composers. This enharmonic modulation uses V7/IV in the key of A♭ major that is then reinterpreted as Ger+6 in C major as the pivot chord.

Here is another example, "Der Neugierige," from Franz Schubert's song cycle, "Die Schöne Müllerin," which was written in 1823, 15 years after the preceding Beethoven example:

The chord on beat 3 in the measure before the double bar line is a secondary dominant—V7/IV—which then becomes the Ger+6 of A♭ major—the resulting key change at 13:41 is delightful and surprising. Schubert modulates from E major to A♭ major using the +6 in A♭ as the pivot chord and again, as in the Beethoven example, the keys are in a chromatic mediant relationship. (Note that the Ger+6 is misspelled—in A♭ the chord's root should be F♭, not E♮, but it was clearly more convenient to dispense with formalities.)

In jazz, we don't find the tritone sub used as a pivot chord to modulate to other keys, and, as shown in Part 1, classical music did not use the dominant 7th as a stable chord—did the two genres simply fail to realize the potential of both of these resources? Given the number of unsurpassed geniuses in both genres, that seems unlikely. Instead, we see aesthetic and cultural values embedded so deeply that composers in both genres adhere to those edicts, entirely unaware of their unacknowledged and unspoken allegiances.

Still, the question remains—why didn't jazz musicians use the tritone sub as a pivot chord in modulations to other keys like classical composers did so often? The answer is twofold—first, jazz musicians, until the mid-1950s, dealt largely with popular music of the time. These tunes were not complicated in terms of form or length—12-bar blues, 16-bar blues, 32-bar form "AABA," etc. The primary value in jazz is improvisation, not formal development. Improvisation requires a predictable "roadmap" for all players to follow, which those song forms provide. If jazz musicians had unique forms that had 85, 89, 123, or 270 measures, like classical music does, the entire genre would come to a grinding halt. The small forms allow jazz musicians to memorize hundreds of them, and they can then successfully engage, instantaneously, with other musicians across the country and the world who share the same repertoire.

So, while jazz has many key changes, those key changes, while interesting, are not the primary focus of the music. For example, the jazz standard "All The Things You Are" by Jerome Kern, from the 1939 musical Very Warm for May, has four different keys in the first 24 measures. Interestingly, the first four keys are the four pitches of the tonic chord, in the correct order no less— A♭maj7: A♭ C, E♭ and G! The fourth key change, to E Major, provides a colorful diversion from the previous four and shows the classical roots of Kern, Gershwin, and others—E major is a chromatic mediant to A♭ major, exactly as found in the previous Schubert example from a century before. (The famous music writer Donald Francis Tovey (1875-1940) called this colorful modulation, which is found regularly in classical music, a "purple patch.")

The modulation back to A♭ at the end of the fourth system from the bottom (Emaj7—C7#5) major is also remarkable—in another nod to the 18C Romantics, Kern uses the Ger+6 chord from E major, C7, as a pivot chord, just like Schumann and Beethoven and virtually every other Romantic era composer. As shown in the example, C7 is the Ger+6 in E, which is reinterpreted as V7/vi to lead us back to the original key. So, we find an enharmonic modulation using the Ger+6 in jazz, but this is rare and does not stand out as a prominent feature of the piece. In contrast, the dramatic Beethoven modulation from A♭major to C major in his Fifth Symphony (above) is structurally important and memorable.

For jazz musicians, these rapid-fire key changes provide a rich and challenging harmonic palette over which to improvise—key changes are just an expected part of the harmonic texture that both listeners and musicians accept as standard practice. In classical music, it is hard to find five key changes in such a short period of time. Key changes in classical music are important not only because they provide variation but also because they play such an integral role in the development and elucidation of the form—form itself is thus a primary value in classical music. In jazz, key changes are important, but the pragmatic concerns of a shared, communal repertoire constrain them, relegating them to a secondary role in the aesthetic values of jazz. In other words, key changes expand the harmonic potential for individual improvisation and group interaction—they are a means to an end, not the end itself. We thus once again see musicians from two genres using the same musical resources in a strikingly similar fashion, another testament to the shared creativity and genius of the magnificent geniuses in jazz and classical music.

In Part 4, the series will end with a look at another sonority, the Neapolitan 6th chord and how it is used (or not used) in both genres.

Special thanks to bassist, composer, and music theorist, Dave Morgan for the invaluable feedback and keen theoretical insights into "All The Things You Are" in particular for this article. And for the countless delightful discussions on these topics over many years that have informed and challenged my perspective on music of all kinds.

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