Fernando Sor’s Etude four is quite simple harmonically. Its most interesting feature is the extensive use of what is called a “pedal point”. This is where a single tone is sustained, usually in the bass but could appear in any voice, through changes of harmony. The pedal point got its name originally through its use by organists who would stand on an organ bass pedal and improvise various harmonic progressions over this sustained tone. It is a very effective way of adding interest and new and unusual dissonance to simple harmonies as you will hear in this study. The pedal point in this piece is either the tonic (G) (measures 1-11 and 33-42) or the dominant (D) (measures 17-32) and appears in the bass or a middle voice. The use of the tonic and dominant tones as pedal points is most typical. Also this feature is not restricted to classical music as it is often heard in jazz as in the opening bars of “On Green Dolphin Street” as recorded by Miles Davis for example.
Other than the pedal point the most interesting harmonic feature is the big German augmented sixth chord that occurs in measure 41 and 42. To review, this chord is typically used as Sor has used it here and involves the interval of an augmented sixth (Eb – C#), found between the two outer voices, that resolves to the octave (D –D, dominant) by moving the voices in opposite directions (contrary motion). The chord sounds exactly like an Eb dominant seventh chord but is spelled differently and functions differently. In this case Eb G Bb C# is the spelling of the augmented sixth chord where as an Eb7 chord is spelled Eb G Bb Db. We would expect the Eb7 chord to resolve down by perfect fifth where as in this case it resolves to (D) or down by half-step as it would in the jazz equivalent tritone substitution. Note that it actually moves into a tonic 6-4 chord before moving to the dominant as it commonly does in classical composition. Remember that the tonic 6-4 chord is considered a dominant with a double suspension.
Also note the discrepancy between the chord implications shown above the staff and the harmonic analysis shown below from measure seventeen through measure twenty-eight. This is a good example of a case in which simple voice-leading (ascending thirds with some chromatic passing tones) can imply various harmonies on the micro level while on the macro level it is clear that this is all a prolongation of the dominant. I was first exposed to this idea of reduction analysis through the work of the great music theorist Heinrich Schenker (1868-1935). In a nutshell, voice-leading is the fundamental principal or force that guides the ear through complex musical passages and if the structural voices are connected by step, combinations of notes will occur along the way that may or may not make sense as independent harmonic structures but will make sense in terms of the voice-leading, taking us from one structural point to another. The idea is we must look at the big picture and not so much the small details. Always ask yourself what is the goal of a certain passage. Most of the time it is best to look ahead in the music and determine the harmonic end point then work backwards to form your analysis.
A couple of other noteworthy features: The use of a tonic chord with an added sixth in measure nine. Sor may not have thought of it in this way as it can also be considered an Em7 chord in first inversion. Yet, to my ear in this context, I would hear it as a tonic G major triad with the added sixth (E). Also note the G minor triad in measure twenty-nine. This is known as a borrowed chord and in my analysis I am hearing it as a minor four chord borrowed from D minor since this entire passage, from measure seventeen through thirty-two, is in the dominant (D) area.
Once again I have included below the performance edition and analytical copy of Etude four for your use. Hopefully this will aid in your understanding and enjoyment of the music.