Etude nine by Fernando Sor corresponds to Estudio thirteen in the Segovia collection of Sor studies. This study is a study in sixths in D minor and has some similarities to Etude six (the study in thirds) in that Sor uses chromatic neighbor notes and chromatic passing tones to alleviate diatonic blandness. As you can see there is not much happening harmonically other than the predictable move to F major (relative major) in the middle (B) section.
The most interesting harmonic features occur first in measure nineteen where Sor uses the Italian augmented sixth chord to move into the dominant (D7) of the supertonic (Gm) and then in measure twenty-three where he uses another Italian sixth chord to move into the dominant (C7) of the relative major (F) creating a circle of fifths progression D7-Gm-C7-F. This chord pattern can also be described as a harmonic sequence in which we have a dominant to tonic progression repeated a step lower. Harmonic sequences usually go hand in hand with melodic sequences as is the case in this piece where the melodic pattern in measures nineteen through twenty-two is repeated with slight variation in measures twenty-three through twenty-six a step lower. This progression with the inclusion of the augmented sixth chords is now a fundamental part of the jazz harmonic vocabulary. The term “tritone substitution” is used to describe this type of harmonic embellishment in which the Eb7 is a tritone substitution for A7 (dominant of D) and the Db7 is a tritone substitution for G7 (dominant of C). Remember that tritone substitutions and augmented sixth chords are one in the same. In a jazz chart the progression would appear as follows:
FMaj7 – Eb7 – D7 – Gm7 – Db7 – C7 – Fmaj7
Of course I have added sevenths to the triads as would be standard procedure in jazz harmony.
The bass in measure twenty-three seems to move by the very unusual (in this period) skip of a tritone (G-Db). The G that we assume to be the bass moves to the F in the following chord and not the Db. This is a case in which we have an implied D bass on beat one of measure twenty-three which would then move down by half-step to the Db and continue to the C in measure twenty-four chromatically, avoiding the tritone skip.
The next feature to note occurs in measures thirty and thirty-two where Sor’s use of chromatic passing tones in the inner voices in parallel sixths (E/C#-F/D-F#/D#-G/E) within the A7 harmony is very much a blues cliché today. Could it be that Sor was the actual father of the blues!?
There are many double suspensions, mainly in the form of 9-8/4-3, that are found throughout the piece that would occur quite naturally where the sixths are suspended over the bar line into the new harmony (measures six, eight, twenty-two etc.). I have indicated only the most prominent occurrence in measure twenty-six.
Lastly, in measures fifty-five and fifty-six on beat four we get a very strong dominant seven flat nine (A7b9) chord. True, it can be considered a full diminished seventh chord on the leading-tone (C#) but there is a very strong A in the bass occurring here. This is not as unusual as you may think as this chord construction was also used quite often by J.S. Bach. It is only natural that this chord type would appear in this period and earlier as it is a logical combination of the leading-tone full diminished seventh chord with the root of the dominant harmony. This is an important realization in determining a voicing for any seven flat nine chord that may come up in our jazz charts. If we understand that the upper four tones of a seven flat nine chord spell a full diminished seventh chord, we can then simply use any diminished seventh chord voicing we already know as a dominant seven flat nine chord with its root missing. I think the easiest way to remember this relationship is, as Joe Pass explains, to play a diminished seventh chord one half-step above the root of the dominant seven flat nine chord. For example:
G7(b9) = Abdim7 or C7(b9) = Dbdim7 etc.
With a bit of practice this will become clear and will become one of the most practical and useful concepts you will ever learn.
Included below are the analytical and performance editions of Etude nine for your use.