Which three main sections make up sonata form?

The three main sections that make up sonata form are:

• Exposition: The initial section where the primary musical subject matter is stated, typically moving from the tonic key to a new key.1
• Development: The section where the themes introduced in the exposition are explored, expanded, and subjected to conflict through tonal flux and thematic fragmentation.12
• Recapitulation: The final section where the principal subject matter is restated, typically resolving the earlier tonal conflicts by presenting the themes in the tonic key.13

While some movements may include an optional introduction or a coda (concluding section), these do not alter the fundamental three-part structure.13