What Is Ternary Form in Music?

Loosely defined, a ternary form has three sections that serve to form the overall structure of the piece. A few types of ternary form exist to help further distinguish one type of ternary from the next. The clarification between different types of ternary form has to do with the way in which sections repeat and the manner in which the music moves through different keys.

Simple Ternary

Simple ternary form consists of three sections that do not necessarily link together through chord progressions. Each section may be a completely different idea. This type of ternary form usually follows the pattern: A B A, where each letter represents a different section and musical idea. Simple ternary has a tendency to be very simple and easy to follow due to the limited changing nature of the thematic material. Music needs a certain amount of repetition to create musical connections, and simple ternary makes this possible. Some popular songs consist of simple ternary constructions, such as "Some Day My Prince Will Come."

Compound Ternary

Compound ternary form also consists of a large three-part structure. The difference comes with the presentation of each section to the audience. Compound ternary consists of three sections, each with a simple ternary form or binary form within the section. Binary forms have only two parts, instead of three. For example, the first section of a compound ternary form with an internal ternary form would have an A B A first section; the second section would be C D C and then a return to the original A-B-A section. If the internal structure were binary, then the form would be A-B, followed by C-D, and then a return to A-B.

Expanded Ternary Form

An expanded ternary form occurs when any section repeats. This form does not include any new material; rather, it simply repeats a previous section. Sonata form uses expanded ternary form to repeat the opening section of the sonata. The A section, usually a binary form, repeats to help establish the tonic of the key. Composers in the classical period would do this to establish the thematic and harmonic implications of the opening section. Most commonly, a repeat sign appears at the end of the A section, instructing the performer to return to the beginning and play the section again.

Other Uses

Ternary form also occurs often in dances, such as waltzes and polkas. The marches of John Philip Sousa almost exclusively contain ternary form structures. Baroque arias often will present an idea, drift off into a new B section and then return to the original theme. The scherzo that appears in many symphonies uses a ternary form, as well as the third movement of most classical symphonies, string ensemble works, and sonatas. All of these forms have a basic three-part construction that uses ternary form.