When scholars discuss Sor's sonata forms we tend to read discussions of the usual suspects: Opp 14 and 15, Op. 22 and 25, and Op. 30. That's as we should expect and delineating the types of sonata forms we see in the multi-movement works of Sor has some valuable scholarly work given to us by Rattanai Bampenyou in a 2012 treatise called A Performance Guide to the Multi-Movement Guitar Sonatas of Fernando Sor and Mauro Giuliani. It was through Bampenyou's dissertation I learned of James Hepokoski and Warren Darcy's Elements of Sonata Theory and William E Caplin's Classical Forms, both fantastic scholarly resources that should inspire debate and further research.
Hepokoski and Darcy's work has been valuable for giving formal articulation to a structural/formal principle I've noticed in Sor's sonatas over the last six years, that there's what the two authors call a "Type 2" sonata, a sonata in which recapitulation of the exposition materials is incomplete. This is a valuable addition to the conceptual lexicon of musicology because it makes an effort at addressing formal patterns in the music we have instead of imposing a one-size-fits-all post-Beethoven theory of what constitutes a "real" sonata form. I have some issues with the specifics of their description of Type 2 sonata and particularly of their objection to the concept of recapitulation because I think they substantially oversell their idea of "rotation"--rotation is a concept that is valuable as a catalyst for new compositional activity, to be sure, but I hesitate to say that the Hepokoski and Darcy concept of "rotation" will help us understand what they regard as Type 2 sonata forms.
In spite of those reservations I believe the basic category of "Type 2" sonatas is valuable and that the most compelling evidence I've seen for it has come from my immersion in the early 19th century solo guitar sonatas composed by Sor, Giuliani, Diabelli, Carulli, Molitor and Matiegka. Up to half of Sor's sonata forms can be described as some kind of "Type 2" approach to sonata form, while Molitor's Op. 7 and the second movement of Matiegka's Grand Sonata II are also explicable as "type 2" sonata movements.
A sonata form Sor composed that to date has not been recognized AS a sonata form by much scholarly literature is the Op. 29, etude 5 in C major. Its brevity and invention are such that if you wanted to make a case for a "textbook" Type 2 sonata understandable by guitarists and non-guitarists alike I think Sor's Op. 29, etude 5 may be one of the best candidates to study.
As you'll see, Theme 1 is indicated with blue notes while Theme 2 is indicated with green notes..
Sor's Op. 29 etude 5 begins with a perky, marching theme in C major. It's a pretty straightforward tonic-to-dominant four-bar melody answered by another four-bar melody that resolves the eight-measure theme with a simple authentic cadence. This theme is immediately repeated, an octave higher, with a second voice providing a contrapuntal accompaniment. For a brief moment Sor has what sounds like the beginning of a brilliant two-part invention. Since this was the 19th rather than the 18th century that's not where things go (alas, for my interests). But it's sufficient to note here that Sor demonstrated that he could compose and arrange contrapuntal music for solo guitar when he wished to. For the sake of our sonata form analysis it's important to stress that we open with an eight-measure theme that is immediately repeated with a contrapuntal development.
The modulating transition begins at the end of the third system and spans 25 measures. That's important to keep in mind in comparison to our eight-measure repeating Theme 1. When Theme 1 is brief and/or has a high level of intra-expositional repetition or expansion of simple thematic gestural cells that can be an indicator that we "may" not get a conventional "full" recapitulation. When Theme 1 material is dwarfed in length by the modulating transition and/or all subsequent material in the exposition that can be another indication (as it is in Diabelli's Op. 29, No. 3 Guitar Sonata in F major) that we're going to get a truncated recapitulation that omits Theme 1.
Theme 2 arrives at the start of system 8. It's a jaunty rising-fourth march theme and this 12-bar line resolves into what I call Group 2, a kind of closing/coda phrase that is presented twice, giving Theme 2 an abb structure. Notice that this Theme 2 material is 24 measures long, three times as long as our unadorned theme 1.
I can't help but mention how few stylistic adjustments you'd need to make to this sonata by Sor to transform it into ragtime material. There can be a lot of ways in which the stylistic elements of what we recognize in ragtime existed in embryonic form in the music of Sor. That's just me speculating for the sake of future compositions.
So we get to Sor's development and he opens with a fun gambit, presenting Theme 1 as a lower-voice subject against which a form of his Theme 2 is presented as a countersubject. We could speculate that the linear trajectory of Theme 2's opening march phrase could be extrapolated from implications in the accompaniment line in Theme 1. It's not as though Haydn weren't known to transform accompaniment patterns in a first theme into the basis for a thematic idea in Theme 2 in any of his sonatas, right? I propose that we can see a comparable creative process afoot in Sor's etude. He shows off his contrapuntal invention at the start of the development by showing how his Theme 1 and Theme 2 can be presented as contrapuntal subject and countersubject and then works to more conventionally guitaristic textures the closer he gets to the recapitulation.
And the closer Sor gets to his recapitulation the more his developmental material resembles the end of the modulating transition. It's at this point that this can be demonstrated to be a good textbook candidate for what Hepokoski and Darcy call a "Type 2" sonata. In their exposition of the concept they propose that a development will tend to have Theme 1 presented in a substitutional way with transitional development standing in for a formal presentation of Theme 1 in a recapitulation "rotation". I think that case is slightly overstated but in this Sor etude their description is perfectly apt. Sor does create a dominant pedal tone that evokes the cadential preparation activity of the transition to Theme 2 and ...
We get Theme 2 as the start of a recapitulation. Interestingly, as I've highlighted in notes green and blue, Sor presents the core linear motif of Theme 1 as the bass accompaniment pattern to the presentation of Theme 2 in the recapitulation. We can think of this as Sor deciding that for a short etude he would rather just recapitulate the short Theme 1 at the same time he brought back Theme 2. Seeing as he began the development with a contrapuntal presentation of Theme 1 and theme 2 materials, why not do this to signal the start of the recapitulation?
It's known that in sonata forms themes can be reworked and expanded. Sor brings back enough elements of his Theme 1 in the accompaniment patterns for his Theme 2 that he could be said to fulfill the "need" for the recapitulation to have some element of Theme 1. But by making the gestures evocative of Theme 1 contrapuntal support for Theme 2 it can be easy for all but the most alert listeners and score-readers to spot what Sor has done. Remember how we saw that Sor's Group II/Theme 2 material is three times longer than the unadorned Theme 1. Sor working Theme 1 in as contrapuntal support for Theme 2 lets him recapitulate his two ideas simultaneously while subjecting them to new developmental possibilities. It also serves as a fine example of a small scale "Type 2" sonata form for solo guitar. If you wanted a candidate for a "Type 2" sonata that's short this one could work even more effectively than Diabelli's Op. 29, No. 3 sonata.
For an ideal case study of a "Type 3" sonata form for solo guitar that can be read through in just two pages we turn to the Op. 29, 10 etude in E flat major, arguably the tightest, most elegant and efficient of Sor's sonata forms.