Sonata form
A Classical-era structure of exposition, development, and recapitulation, used mainly for first movements of sonatas and symphonies.
Exposition: The opening section stating the main themes, the first in the home key, the second in a contrasting key. The form's first act, where the key conflict that drives the whole movement is set up.
Binary form: A two-part structure in which each half repeats and the second moves away from and back to the home key. Sonata form grew out of binary schemes, adding thematic development in the middle.
Joseph Haydn: Composer of over 100 symphonies who established sonata form's conventions and their playful disruptions. Often called the form's father; his monothematic expositions bend its rules from within.
Sonata: A multi-movement work for one or two instruments, distinct from the form its movements may use. The commonest confusion: the genre named the form, but sonata form appears in many genres.
Sonata cycle: The multi-movement plan of fast, slow, dance, fast that sonata form anchors with its first movement. The form defines the first movement of the standard four-movement design.
Development: The middle section that fragments, combines, and moves themes through shifting keys away from home. Where the exposition's key conflict is dramatized before resolution.
Domenico Scarlatti: Italian keyboard composer whose 550-odd sonatas show early modulating, rounded binary designs. His keyboard sonatas prefigure the exposition-development-recapitulation shape.
Wolfgang Amadeus Mozart: Classical composer whose 41 symphonies and piano concertos display sonata form at its most polished. His expositions balance sharply characterized first and second themes.
Rondo form: A structure alternating a recurring refrain with contrasting episodes, typical of final movements. The era's other major form; sonata-rondo fuses the two.
Sonata theory: James Hepokoski and Warren Darcy's analytical system of defaults, deformations, and formal zones. The form's most influential modern theory, built on its norms and their violations.