ternary form
A musical structure with three sections where the first returns, ABA.
In Depth
Ternary form (ABA) is a three-part structure where the first section returns after a contrasting middle section. The return of A provides a satisfying sense of symmetry and closure, while the B section offers contrast in key, mood, texture, or all three.
Ternary form is one of the most common structures in music, found in everything from pop songs to concert arias. The da capo aria is essentially ternary form with an ornamented repeat. The minuet and trio is a compound ternary form (each section is itself in binary or small ternary form). Simple as it is, ternary form provides a deeply satisfying balance of variety and unity.
The da capo aria — opera's signature vocal form for over a century — is essentially ternary form with built-in improvisation. The return of A was the singer's moment to dazzle.