How does three-part form use contrast and restatement?

In musical composition, three-part form—also known as ternary form—is defined by a symmetrical aba structure that relies on the interplay between thematic statement, contrast, and return.12

• Statement (A): The composition begins with an initial section that establishes the primary musical material.12
• Contrast (B): The second section introduces contrasting material, often characterized by a different lyrical quality, character, or tonality (key). This section provides a departure from the opening, creating tension or variety.1234
• Restatement (A): The final section involves a return to the initial material. This restatement may be a literal repetition or a varied version of the first section, providing a sense of resolution and formal balance.243

While some may confuse this with sonata form, which also features three sections, sonata form is a more complex structure that evolved from binary form and relies on the dialectical development of themes rather than simple contrast and restatement.12