Churgin, Bathia (Summer 1998). "Beethoven and the New Development-Theme in Sonata-Form Movements". The Journal of Musicology. 16 (3). St Joseph, Michigan: Imperial Printing Company: 327–9. doi:10.1525/jm.1998.16.3.03a00030. JSTOR763994. As the author notes, the practice of including new material in the central section of a ternary-form (sonata) movement is not a Beethoven innovation- there are examples in and preceding Mozart's music.
Aber, Adolf (May 1956). "Beethoven's Autographs". Musical Times. 97 (1359). The Musical Times, Vol. 97, No. 1359: 249–251. doi:10.2307/936460. JSTOR936460.
Churgin, Bathia (Summer 1998). "Beethoven and the New Development-Theme in Sonata-Form Movements". The Journal of Musicology. 16 (3). St Joseph, Michigan: Imperial Printing Company: 327–9. doi:10.1525/jm.1998.16.3.03a00030. JSTOR763994. As the author notes, the practice of including new material in the central section of a ternary-form (sonata) movement is not a Beethoven innovation- there are examples in and preceding Mozart's music.
Aber, Adolf (May 1956). "Beethoven's Autographs". Musical Times. 97 (1359). The Musical Times, Vol. 97, No. 1359: 249–251. doi:10.2307/936460. JSTOR936460.