Etude five by Fernando Sor is the most ambitious harmonically so far. This study is reminiscent of the first prelude from the Well-Tempered Clavier by J.S. Bach. Sor makes extensive use of the full diminished secondary leading-tone seventh chord as a way of drawing out or delaying expected cadences. For example, we would expect to find a D7 chord on the third beat of measure seven resolving to G major in measure eight. Instead Sor writes a C#dim7 taking us to D in measure eight delaying the expected resolution to G until measure ten. He does the same thing in measures sixteen, seventeen and eighteen where the phrase is extended by the use of three secondary leading-tone chords. Each time it comes as a surprise to the ear which keeps things interesting and gives us some asymmetry in that it creates unusually long and irregular phrases rather than the traditional eight bar patterns.
I really like the way he moves into D minor (ii) beginning in measure twenty-one. Notice how the bass descends step-wise (E - D -C#) while the alto ascends step-wise (C - D- E) setting up the A7 chord (dominant of D minor) in measure twenty-two. The introduction of the Bb in measure twenty-one which moves to the root (A) in measure twenty-two is what really pulls us into the new key since of course this is the key signature of D minor (the C# is the new leading-tone from harmonic minor). To take us back to tonic the D minor becomes the (ii) chord in C major with the nice chromatic voice-leading in measure twenty-five to twenty-six (A-Ab-G) in the tenor. Harmonically this Ab alters the (ii) chord, changing the quality from minor to diminished. It is then considered a borrowed chord from the parallel minor key of C minor. Altered chords are usually found in a context of voice-leading involving chromatic passing tones in one or more voices. Here again the voice-leading is fundamentally the most important thing to notice. Get used to observing how the individual voices move smoothly through the piece. I am always fascinated with the way great composers can move through complex harmonies and multiple key changes while maintaining the fundamental principles of good voice-leading. This no doubt is a product of excellent training in counterpoint. I remember my first class in counterpoint was a revelation to me as to how music was actually composed. Harmony is a by-product of sound contrapuntal principles. Great composers, at least in the tonal period, were always primarily concerned with voice-leading and counterpoint, or the way individual voices related to each other according to the concepts of consonance and dissonance, when writing music. I always thought counterpoint should be the first course of study in music school. If you are interested in pursuing this study pick up The Study of Counterpoint from Gradus ad Parnassum by Johann Joseph Fux (1660-1741) translated and edited by Alfred Mann, published by W.W. Norton and Co. New York. This is an eighteenth century text (1725) that was used by Bach, Haydn, Mozart and Beethoven to name a few and is the best little book I have seen on the subject.
Note the use of the tonic (C) pedal point in the opening four measures and from measure forty to the end. Also as is common in many of Sor’s pieces is the use of suspensions which delay the resolution to tonic as can be seen in measures twenty-four, thirty-six and forty. The two most active tones of the A7 (C# and G) and G7 chords (B and F), which together form the highly unstable tritone, are suspended over from the preceding measures while the bass moves to tonic. These two tones do finally resolve as they should to D and F and C and E respectively by beat four of the measure.
As usual I have included an analytical and performance version of Etude five below.