This article explores the phenomenon of structural expansion in Beethoven's mid-term sonatas and its historical significance in redefining the classical paradigm. Through a detailed analysis of representative works such as the Waldstein Sonata (Op. 53), the Kreutzer Sonata (Op. 47), and the Passionate Sonata (Op. 57), research shows that Beethoven expanded the length of the exposition, increased the diversity of themes, and broke tone symmetry. These innovations reflect a profound philosophical shift from Enlightenment rationalism to romantic subjectivity. The article advocates that Beethoven's formal experiment is not only a technical adjustment, but also a profound artistic response to individual and expressive changes, laying the foundation for romantic music aesthetics.
Xiaolei Zhang (2025) studied this question.