After the classical period helped to define the sections of the sonata-allegro form, composers began to use the general idea of the form and get away from the strictures. The first composer to really reshape sonata-allegro form was Beethoven at the beginning of the Romantic period in the early 19th century. Beethovenís sonata-form movements are still organized around the two tonal areas of the past. However, he breaks with tradition in almost all other aspects of the form.
First, Beethovenís themes are not clearly discernable. One transitions into another seamlessly and are related through smaller units, called motives, rather than large sweeping musical gestures. As well, Beethovenís works had largely expanded development sections and also very long codas at the end. In both the development and the coda, he would break fundamental rules and introduce new material that was not heard first in the exposition. Finally in works like the his Waldstein Piano Sonata, instead of the secondary key area being five steps above the first key, Beethoven went to the key only three steps above.
From these changes, composers continue to use sonata-allegro from in reinvented ways. Antonin Dvorak used a modified sonata-allegro form for the first movement of his Cello Concerto No. 1. In the Dvorak work, the second theme never appears in the development section, however new material is introduced there. As well, in the recapitulation, the second theme returns first then followed by the opening theme.
In the late romantic composers, like Mahler at the turn of the 19th century, composers no longer felt obligation to maintain the one to five relationship of the two themes as well the contrast between the two themes became more and more drastic. In his Symphony No. 1, Movement 3, the first theme of the work is a version of the melody Frere Jacque and the second theme is a Jewish melody.
Composers continue to use sonata-allegro form as a means to organize their music. In contemporary music, the form no longer hold the same implications as before to establish irony and defy audience expectations, but composers still are able to find new context for this established form.