Kurt Schwitters composed this poem in 1922 to show that musical form can be applied to language. The poem consists of four movements (with a cadenza in the fourth), as well as an overture and a finale. Like music it introduces and varies themes — the first movement, in sonata form, develops four main subjects; the largo and the scherzo both have an ABA form; and themes from the first movement reappear in the scherzo. But fundamentally it’s a work of language rather than music — the performer is speaking rather than singing.
“In the first movement I draw your attention to the word for word repeats of the themes before each variation, to the explosive beginning of the first movement, to the pure lyricism of the sung ‘Jüü-Kaa,’ to the military severity of the rhythm of the quite masculine third theme next to the fourth theme, which is tremulous and mild as a lamb, and lastly to the accusing finale of the first movement, with the question ‘tää?’”
Schwitters said he included a written cadenza for those who “had no imagination,” but he preferred that the performer improvise based on the piece’s themes.
from Futility Closet https://www.futilitycloset.com/2017/11/14/the-ur-sonata/