Binary form divides a piece into two sections, each typically repeated. It is the foundation of Baroque dance movements, the seed of sonata form, and the structural logic of hundreds of popular songs and folk tunes.
TWO SECTIONS: A AND B
Binary form divides a musical piece into two sections, both typically repeated: A (often repeated), then B (often repeated), producing the overall scheme ||: A :||: B :||. The two sections share thematic material and are harmonically interdependent — the A section typically ends in a key other than the tonic (often the dominant in major keys, the relative major in minor keys), creating the expectation that the B section will return to the tonic. Binary form is the structural logic of Baroque dance movements (allemandes, courantes, sarabandes, gigues, minuets), late Baroque keyboard sonatas (Domenico Scarlatti), and early Classical keyboard movements.
The repeat signs are not decorative. The repetition of each section was a standard performance practice that allowed listeners to absorb the formal architecture twice and gave performers an opportunity to embellish the second time through. In Bach and Scarlatti, the repeated playing is often the moment for spontaneous ornamentation; in Mozart and Haydn it may simply confirm the formal symmetry.
SIMPLE VS. ROUNDED BINARY
Two types of binary form are distinguished by whether the opening theme returns at the end of the B section:
- Simple (continuous) binary: the B section does not return to the opening theme — it develops the material and arrives at a concluding cadence in the tonic with whatever material it has. Common in Baroque dance movements.
- Rounded binary: the B section begins with developmental material (often in a related key) but concludes with a return of the A section material in the tonic — creating an ABA' structure within the nominal AB frame. The opening returns "rounded off" by the end.
- Balanced binary: a sub-type in which only the closing portion of A (often the cadential material) returns at the end of B, balancing the two sections by sharing a common cadential ending.
Rounded binary form is particularly significant because it is the structural ancestor of sonata form. Many theorists (including Charles Rosen in The Classical Style and Hepokoski & Darcy in Elements of Sonata Theory) argue that Classical sonata form evolved directly from rounded binary form: the A section becomes the exposition; the first part of B becomes the development; the return of A becomes the recapitulation. Many late-Baroque and early-Classical keyboard sonatas (C.P.E. Bach, Domenico Scarlatti, the young Haydn) show this evolution in progress.
HARMONIC TRAJECTORY
The harmonic logic of binary form is precise and universal. In a major-key binary movement: A begins in tonic, modulates to the dominant, ends on a PAC in the dominant; B begins in the dominant, modulates through related keys (often reaching the supertonic minor or the submediant), returns to tonic, ends on a PAC in the tonic. In a minor-key binary movement: A begins in tonic minor, modulates to the relative major (III), ends on a PAC in the relative major; B explores related keys (often the dominant minor or subdominant minor) before returning to tonic and ending with a PAC there. The B section is usually the longer of the two sections in a developed binary form, because it must do more harmonic work — exploring distant keys and returning home.
BAROQUE DANCE SUITE AS BINARY FORM
Johann Sebastian Bach's keyboard suites (French Suites, English Suites, Partitas) consist entirely of binary-form dance movements. Each dance — allemande, courante, sarabande, gigue, plus optional galanteries (minuet, bourrée, gavotte, passepied) — is a binary form with specific tempo, meter, and character:
- Allemande: moderate, duple, with an upbeat and continuous eighth-note texture; the suite's opening movement.
- Courante: faster, triple, with flowing line; the French type uses hemiola at cadences, the Italian (corrente) is faster and lighter.
- Sarabande: slow, triple, with characteristic accent on beat 2; the emotional centre of the suite.
- Gigue: fast, compound meter (6/8, 12/8, 9/8), with energetic leaping figures; the suite's exuberant close.
- Minuet, Bourrée, Gavotte, Passepied: optional intervening dances of varying tempos and meters.
Studying these dances in order, with scores, is one of the most efficient introductions to binary form and its variations. Bach's Partitas are particularly rich, expanding each dance with elaborate ornamentation and counterpoint while maintaining the strict binary form.
SCARLATTI'S 555 SONATAS
Domenico Scarlatti's 555 keyboard sonatas (catalogued by Ralph Kirkpatrick) are nearly all in binary form. Together they constitute the largest single-composer corpus of binary-form music in existence and an inexhaustible study resource. Many of Scarlatti's sonatas are paired (slow-fast or fast-slow) and prefigure the two-movement sonata; some have strikingly modern features (cross-rhythms, hand crossings, dissonant sevenths, evocations of Spanish folk music). The K. 87 sonata in B minor is a melancholy continuous binary; the K. 141 sonata in D minor is a virtuosic moto perpetuo binary with simulated guitar strums.
THE MINUET: BINARY WITHIN TERNARY
The Classical minuet demonstrates a fascinating nested formal structure: the overall movement is ternary (Minuet — Trio — Minuet da capo), but each of the three sections (Minuet, Trio, Minuet) is itself in rounded binary form. So the formal structure is: ||: A :||: BA' :|| — Trio: ||: C :||: DC' :|| — Minuet da capo (without repeats). This nested structure creates the satisfying large-scale proportion of the Classical minuet.
The Trio (so called because it was historically scored for three instruments) provides contrast in scoring, key, and character. The Minuet da capo (from the head) repeats the original Minuet, usually without its internal repeats, and provides a sense of formal closure through return.
OTHER BINARY APPLICATIONS
Binary form is not confined to Baroque and early-Classical instrumental music. Hymns and chorales often have binary structure (a first phrase ending on the dominant, a second phrase ending on the tonic). Many folk songs and pop songs follow the same harmonic logic. The 32-bar AABA jazz standard form can be analysed as a binary form with an internal repeat: ||: A :||: B A' :||, where the second section consists of contrasting bridge plus a return of A — a rounded binary at the level of the chorus.
SOURCES & FURTHER READING
- Rosen, Charles. The Classical Style. Norton. Chapters on binary form and the minuet.
- Caplin. Classical Form. Oxford University Press. Chapter on Binary and Ternary.
- Open Music Theory — Binary and Ternary Form (openmusictheory.net, CC BY-SA 4.0).
- IMSLP — Bach French Suites, Domenico Scarlatti Sonatas (imslp.org).
- Ratner. Classic Music. Schirmer. Chapter 4: Binary Form.
- Kirkpatrick, Ralph. Domenico Scarlatti. Princeton University Press, 1953.