Where to cut off a sonata theme for Theme and Variations?
I am thinking of writing a Theme and Variations based on a sonata. With sonatas, I tend to gravitate towards the first movement, which is most often in sonata form, and this poses a bit of a problem. Namely, where to cut off the theme and start variations? With rondos and symphonies, this cutoff point is clear, but for different reasons. In a rondo, it is clear because it is the section that comes back multiple times. In a symphony, it is clear because of orchestrational changes that coincide with the change in theme.
With piano sonatas, not really, especially Mozart sonatas. Obviously, I would be including the first theme, but often the first theme ends on a half cadence, and the transition ends on the same chord as that half cadence, but is modulating in the process. This is what gives the smooth movement from one theme to the next in a sonata. So the first theme on its own or even combined with the transition feels like an incomplete entity, like it has been amputated, even at the last phrase ending. But I don't want to include the entire sonata exposition if I don't have to. Especially because the second theme tends to be more developmental than the first theme anyways.
As an example, take Mozart's Piano Sonata in F major K 280. These are the 2 possible cutoff points that don't include the more developmental second theme:
Either way, I'm going to have to add an F major chord at the end of the theme. I don't feel comfortable ending a melody at a half cadence or a modulation to the dominant, just to repeat the entire melody with embellishment, because then it feels like every variation is incomplete. But where should I cut off the theme, add the F major chord, and start the variations? At the end of the first theme and before the transition? Or at the end of the transition before the second theme arrives?
On the one hand, if I cut it off at the end of the first theme, I don't have to worry about embellishing triplets or having it feel too developmental(like mid theme developmental, not variation developmental). On the other hand, if I cut it off at the transition, I have more wiggle room for variations and thus can probably do more variations than if I just have the first theme alone. Mid theme development is also one of many reasons I don't usually use the slow movement as my source of melodic and harmonic material in a Theme and Variations.
So, once I figure out what sonata I want to do a Theme and Variations on, where should I cut off the theme, add a tonic chord, and start writing the variations? Should I cut it off at the first theme to avoid too much mid theme development? Should I cut it off at the transition to have more wiggle room for variations? Or should I let the length of the first movement of the sonata dictate that for me(long exposition, just the first theme, short exposition, first theme and transition)?
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You find a sonata (or sonatina) by a composer who wasn't very adventurous, and wrote music in nice textbook-like 4 8 and 16 bar phrases and sections.
That mostly rules out the Haydn, Mozart or Beethoven, but there are plenty of lesser known ones (though bear in mind they are lesser known for a reason!)
Michael Haydn, Leopold Mozart, Dittersdorf, Boccherini, Cimarosa, Salieri, Clementi, Pleyel, Hummel, Czerny, etc, etc...
...often the first theme ends on a half cadence...
I think you have mislabeled the cadence ending the first group of themes. It should be...
...where mm. 12-13 is a PAC in F.
At that point there is an elision in m. 13 where the transitional phrase takes up a triplet figuration an modulates from F to C.
It seems strange to select the transitional phrase for theme and variations.
From a structural point of view variations are based on small binary forms, because they present brief but complete ideas. Being complete they don't suggest something else is about to happen, but then never does. Repeating a transitional structure may set up a frustrating transition that never goes anywhere. It could end up sounding like a person repeating: "please allow me to introduce myself, my name is... please allow me to introduce myself, my name is..."
From a purely structural view you could play the first 12 bars and simply end on the F major chord of m. 13. Just hit the full chord but don't continue with the triplets.
The opening often just presents a bunch of short phrases in the tonic without modulating. This would seem to be a better place to play around with variations.
K 330 actually provides an example of how the initial statement on the tonic invites variation...
Maybe K 330 provides a kind of model to follow?
You could present the open theme on the tonic re-interpreted with different rhythmic figurations.
I'm not sure that you can do a whole set of variations that way, but that is a different matter.
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