Which part in the sonata cycle typically includes transformations of melody, harmony, and rhythm?

The development section of the sonata cycle is where the composer takes the themes presented in the exposition and transforms them through various musical techniques. This part of the structure is characterized by experimentation and exploration, often featuring changes in melody, harmony, and rhythm. The composer may manipulate themes by altering their intervals, switching keys, or varying the rhythmic values, creating contrasts that enrich the overall narrative of the piece.

In contrast to the exposition, which introduces the main themes, the development delves into deeper and more complex interactions between them. It is a crucial part of the sonata form that allows composers to create tension and drama before returning to the stability of the recapitulation, where themes are restated in their original forms. The coda, while it may provide closure to the piece, typically does not involve the same level of transformation as seen in the development.