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Ternary form is a musical form consisting of three distinct sections with an ABA pattern of large-scale repetition: an opening section (A), a contrasting section in the middle (B), and then a return to the material from the opening section (A). (Though it might seem logical to call ABC ternary form as well, it is more often considered through-composed because each section contains different music.)

As shown in Example 1, each section in ternary form may immediately repeat, either with repeat signs (most commonly) or written out. However, A and B do not repeat together, and neither do B and A.

Example 1. Abstract diagram of ternary form with common repeat structure.

Structure of Individual Sections (Simple vs. Compound)

While the contents of each section can vary greatly concerning phrase and form, each section commonly comprises multiple phrases, and very often those phrases combine together into a complete form (very often a binary form). A ternary form is considered to be compound (or composite) if one or more of its sections comprises a complete musical form. If a section does not contain a complete form, it can be called simple. In many compound ternary forms (like minuet & trio or scherzo & trio in particular), all sections contain complete forms (often rounded binary form). In compound ternary forms of the 19^th century, however, the last A section is often shortened and is simple, not compound.

Example 2. Abstract diagram of a compound ternary form where all sections contain their own complete form.

Example 3. Hypothetical example of a compound ternary form where all sections contain their own complete forms.

Example 4. Diagram of a ternary form where only the first section of the form comprises its own complete form. See Chopin’s Mazurka in A minor, Op. 17, no. 4 for an example of this.

Contrasting Characteristics of B

The second section of a ternary form, usually referred to as the B section, is expected to provide contrast with the A section that preceded it. This contrast may come from a variety of musical domains including key, mode, texture, time signature, rhythmic ideas, melodic ideas, range, instrumentation, register, and so on. The length of B, however, is expected to be generally proportional to that of A.

Stability of Each Section

In some genres (like the minuet & trio), the A and B sections exhibit a relatively similar level of stability, usually because they start and end in the same key and contain phrases that are tight-knit. In other genres (arias in particular), the B section is often less stable than A. B‘s instability is largely due to starting and ending in different keys and having a generally looser phrase-structural organization than A.

Keys and Harmony

Closed and Open Harmonic Endings

As with other forms, each section can be described in terms of being harmonically open or closed.

Modulation within a Section

Modulation is possible within each section in ternary form, but it is very rare in the A section and should be considered atypical when found there. Modulation in the B section is much more likely to be found in an aria than in dance forms like the minuet and trio.

Auxiliary Sections

Like other forms, ternary form can contain auxiliary sections. Small transitions, small retransitions, small prefixes, and small and large suffixes are common. See the chapter on Formal Sections in General for more information on auxiliary sections.

Example Analyses

https://musescore.com/user/32728834/scores/8414264/embed

Example 1. Frederic Chopin, Polonaise in A major, Op. 40, no. 1 – Click to See Score (PDF)

Example 2. George Frideric Handel, “Waft Her Angels” from Jephtha – Click to See Score (PDF) – Audio

1. Bernhard Crusell – Clarinet Quartet, Op. 7, III, Menuetto (.pdf, .docx). Access score and audio.
2. Josephine Lang – Traumbild, Op. 28, no. 1 (.pdf, .docx). Access score and audio.