How did Beethoven enlarge the scale of Classical sonata form?

Ludwig van Beethoven significantly enlarged the scale of the Classical sonata form while retaining its fundamental principles. His approach to expanding the form included several key structural innovations:1

• Expanded Exposition: Beethoven significantly increased the length of the exposition and frequently utilized unusual keys within it.1
• Extended Coda: He elevated the importance of the coda, often expanding it to such a degree that it functioned almost as a second development section.12
• Developmental Scope: He utilized the development section to expand the overall scale of large movements, sometimes introducing new thematic material to provide relief or further the musical argument.3
• Structural Weight: Beethoven pioneered the principle of transferring structural weight from the first movement to the finale, a practice that became highly influential for later composers.4

While he maintained the basic framework of the form, his later works began to shift away from the dualistic sonata principle, moving back toward the monistic approach found in variation form and fugue.1