Sor Op. 25, first movement
Theme 1 is merely eight measures long and leads into a modulating transition in the second half of measure 8. As short as this theme appears to be on the page the Andante Largo tempo has to borne in mind. The harmonic rhythm is explicable in terms of half notes so that one measure of 4/4 at this tempo could cover what would proportionally be two measures of 4/4 in a livelier tempo.
With that proviso in mind the first theme is a straightforward call and response. The first phrase starts on the tonic and ends on the dominant, the second phrase starts on the dominant and resolves to the tonic. By beat 2 of measure 8. The spare texture shouldn't dissuade us from affirming that Theme 1 resolves in the first half of measure 8 with an authentic cadence of the sort we would expect in a first theme in a sonata form in the early 19th century. There's no requirement that the authentic cadence be on a downbeat or be a perfect authentic cadence of the cumulative development and resolution of thematic ideas is explicable in such a direct, call and response eight-measure pattern.
You'll be able to consult the score below.
The modulating transition begins at measure 9. Sor takes eighteen measures to finally affirm an authentic cadence in E flat major (bottom system of page 1, indicated in green). Using a series of circle progressions, Sor modally mutates each arrival point at a major triad into a parallel minor triad that prepares the next sequence in the modulating transition. So G major mutates into G minor, which becomes the springboard for the next modulating phrase into F major; F major mutates into F minor and prepares a phrase that modulates into E flat major and it is at this point that Sor begins to postpone his cadential arrival that affirms that E flat is the new key for the next theme. As is fairly typical of guitarist composers he feints arrival until the third pass at the authentic cadence in the target key/target cadence (we'll see that Molitor and Matiegka do this in their sonatas). But since even this authentic cadence has a rhythmically weak arrival Sor repeats the entire cadence-establishing phrase with his pedal tone work transposed up an octave. It's only at the bottom of page 1 that Group II really begins, with its first theme indicated in orange.
Theme 2 (aka Group II, Theme 1) is actually more or less a rhythmic diminution and melodic decoration of Theme 1 from the start of the sonata. The melodic/harmonic activity is still a I-V followed by a V-I phrase structure only this time the call and response is made much more explicit by Sor having each "call" sounded on the treble strings in the first half of a phrase given an "answer" on the bass strings while simple pulsing thirds punctuate the middle of the voices as accompaniment. This simple but effective compositional device allows Sor to evoke a symphonic overture without having to deploy more than the leanest available textures.
It's also a simple enough of a process that in the second phrase Sor embellishes the initial idea of Theme 2 for some added drama. Phrase 3 introduces secondary dominant functions and more of an aria/solo texture, as though a star vocalist were declaiming the climax of this part of the theme before the orchestra comes back to resume accompaniment. Phrase 4 gets us there, and the "orchestra" texture returns in Group II, Theme 2 aka the closing theme that will lead into the coda. This theme (indicated in red) evokes more explicitly the rhythms of Theme 1 from the start of the exposition. This intra-expositional callback, combined with the obvious similarity of Theme 2 to Theme 1 will go a long way to explaining what happens in the recapitulation of this sonata form.
The development begins with a D flat tutti that prepares a phrygian-inflected half cadence arrival on a C major chord. We're clearly not to consider this chord as a tonic because the D flat chord destabilized the tonality too much. This is preparation for an arrival at F minor, which we get in system two of page 2.
From here the development evokes the double dotted rhythms of Theme 1 and builds up slowly and steadily to a dominant pedal that gets us to ...
Group II, Theme 1. Sor does not bring back Theme 1 and instead brings back his Group II material, if in a slightly truncated form. The Closing Theme/Coda returns but then we've noted how the closing theme evokes the Theme 1 dotted rhythm melody. There was no point in bringing back Theme 1 since it was conceptually built into the closing theme/coda.
At one point I considered this sonata to have a kind of reversed recapitulation in which Theme 1 came after Theme 2 but the melodic turns in the closing theme are too distinct for me to still endorse my earlier view. Instead I would now propose that what we're hearing here is what Sor has done in his Grand Sonatas, which is to eliminate whatever redundancies he considered in the exposition. Theme 2 being a derivation of Theme 1, and the closing theme being a recall to Theme 1, the entire movement can be thought of as almost a developing variation on a single set of ideas that is cast in a sonata form so as to be an overture for the following movement.
One of the things we've been able to notice as we go through Sor's sonata forms is how short his development sections are and how frequently he simply drops materials that appeared in his expositions when composing his recapitulations. Given the extent to which Sor subjects his gestures to intra-expositional development and the degree to which his first and second group materials are often observably outworkings of common melodic and rhetorical formulas, I would suggest that the reason Sor's developments are so often short and he favors incomplete or truncated recapitulations is because, in addition to contending with the significant physical limitations the guitar presents to realizing a sonata form, he wanted to avoid a more "textbook" approach to his ideas because they would otherwise overstay their welcome (and make the pieces vastly longer and more difficult to play than they already are).
In the case of the Op. 25 careful study shows that we're looking at a sonata form that is really a gigantic prelude to another movement, which in this case will turn out to be another sonata.