Diabelli Op. 29, Sonata in C major
This is the first and weakest of the three Op. 29 sonatas for solo guitar composed by Diabelli. The first movement may provide the simplest evidence for my assertion. Movements two through four are solidly made (rounded binary, menuet and rondo forms) but the opening sonata sticks out like a sore thumb. It's on the basis of the opening sonata form that I regard this as the weakest of the three guitar sonatas but it may be a useful case study through which to demonstrate that even in the early 19th century it was well within compositional norms to have a sonata form with a Theme 1 in an exposition that never comes back in the recapitulation. The fact that Diabelli botched this where Chopin didn't shouldn't distract us from the fact that if both Diabelli and Chopin tried their hands at this approach to sonata form that it may not have been as non-normative as would later be implied by the prescriptions of books promulgating ideas about what sonatas should be.
One of the expectations in a sonata exposition in a traditionally tonal sonata is that we will hear a cadence of some kind that confirms we've arrived at the end of the first theme or thematic group. Often we can expect this to be an authentic cadence. If we get a half cadence, as we famously do at the end of the first theme in Beethoven's Fifth, we expect to hear something come afterward that signals we are moving forward to the next thematic idea.
Well, Diabelli didn't do that. He sets up an eight-measure theme that ends on a half cadence that sounds like it might be the first half of a parallel periodic theme. But instead of completing the periodic structure moving forward from the half cadence in measure 10 he jumps straight into what turns out to be not a modulating transition but his actual Theme 2. I kept wondering the first few times I listened to this sonata and read through the score whether I was hearing and looking at a modulating transition or Diabelli REALLY intended this new idea in which a G major chord moves to an E major chord that moves to A minor and D major and began to prepare an authentic cadence in G major was NOT modulating transition material but, in fact, Theme 2.
The material from measures 11 through the end of the exposition (up to the repeat sign) really are Theme 2 or the Group II material in this exposition. It took me poring over the score to see how the Group II material is recapitulated starting at measure 43 to the end of the movement in order to recognize that Diabelli composed a truncated recapitulation in which he omits his Theme 1 material. But I couldn't recognize this the first half-dozen times I listened to and read through the piece, score in hand, because in harmonic/linear terms Diabelli's Theme 1 was never more than the first half of a theme, a theme he never actually completed. And coming to the realization that Theme 2 arrives with no preparation and no modulating transition made it tougher to recognize that it and the closing theme/coda material were part of a sonata form--I had to study the sonata for quite some time before I began to recognize how it was a sonata but recognizing it on a sonata hinged on my recognizing that Diabelli did two very basic things in this that made it impossible to recognize as a sonata form based on three traditional textbook assumptions.
1. Theme 1 ends on a strong cadence that clearly signals a periodic or sentence structure is resolved
2. There's always a transition to an identifiable Theme 2
3. A sonata recapitulation MUST bring back everything from the exposition in the order it appeared
NONE of these assumptions apply to Diabelli's Op. 29, No. 1. Now I'm perfectly willing to say this makes the sonata movement in the work a WEAK sonata but it helped me to discover that the gap between textbook prescriptions about what a sonata form even IS and what it can be observed to be in the actual literature for the guitar can be large. I began to conclude over the last five years that it made more sense to continually modify my understanding of what counted as a sonata form and what "ought" to happen by what composers actually did in 18th and early 19th century music rather than stick to what post-19th century theoreticians said made for a sonata form.
Diabelli, it must be said, isn't the only guitarist composer who availed himself of the shortcut of playing what feels like half of a first theme whose half-cadence leads to a transition into a Theme 2 in the dominant key. Francois (aka Francesco) Molino also does this in his Op. 6 guitar sonata No.1, for instance, and you can hear a performance of the work over here . But where Molino does his bait and switch in transforming the second half of his Theme 1 material into a modulating transition into his Theme 2 he does us the favor introducing Theme 2 in the bass strings. Theme 1=treble melody, Theme 2=bass melody is a nice, direct way of signaling that we've got ourselves a sonata exposition even if it could be argued Molino took a shortcut by not "finishing" his Theme 1. But Molino does in his Op. 6 guitar sonatas what Diabelli did not do in his Op. 29, No. 1 guitar sonata, present our ears with a strong delineation of thematic groups inside a short exposition.
To a lesser extent Molitor ends his Op. 12 guitar sonata with such a weak authentic cadence on measure 8 of his first theme that his swift move to modulate to Theme 2 sounded for months like it, too, was a case of not really finishing his Theme 1 before trying to get to Theme 2. This impression was also heavily reinforced for me by Molitor's use of a dominant pedal point in the new key (G major) that kept sounding to me like he was setting up the dominant of the dominant to usher in Theme 2. That might have been a reasonable expectation for someone immersed in sonata forms by Haydn, Beethoven or Mozart, but for guitar sonatas this misled me. I didn't realize that Molitor was pretty confident his auditor would here Theme 2 as the Theme 2 it can be identified as being in the score ... but not necessarily to a 21st century ear. But even compared to Molitor's Op. 12 or Molino's Op. 6, No. 1 what Sor did seems sloppy. Molino and Molitor made a point of recapitulating their Theme 1 materials and led them through to some logical conclusions, something Diabelli didn't do in his Op. 29, No. 1.
The blunt and colloquial take-away from all this is that if we wanted an example of why a composer like Beethoven might have regarded Diabelli as a mediocre hack this would be a work that could be provided as evidence for that judgment.
Fortunately, the No. 2 and No. 3 guitar sonatas have stronger sonata forms.