Ternary form, sometimes called song form, is a three-part musical form

Musical form

The term musical form refers to the overall structure or plan of a piece of music, and it describes the layout of a composition as divided into sections...

, usually schematicized as A-B-A. The first and third parts (A) are musically identical, or very nearly so, while the second part (B) in some way provides a contrast with them. The B section is often called the trio

Trio (music)

Trio is generally used in any of the following ways:* A group of three musicians playing the same or different musical instrument.* The performance of a piece of music by three people.* The contrasting section of a piece in ternary form...

, especially in minuet

Minuet

A minuet, also spelled menuet, is a social dance of French origin for two people, usually in 3/4 time. The word was adapted from Italian minuetto and French menuet, and may have been from French menu meaning slender, small, referring to the very small steps, or from the early 17th-century popular...

s and scherzi

Scherzo

A scherzo is a piece of music, often a movement from a larger piece such as a symphony or a sonata. The scherzo's precise definition has varied over the years, but it often refers to a movement which replaces the minuet as the third movement in a four-movement work, such as a symphony, sonata, or...

.

Characteristics of the form

In ternary form, unlike the rounded binary form

Binary form

Binary form is a musical form in two related sections, both of which are usually repeated. Binary is also a structure used to choreograph dance....

, each section will usually be self-contained both thematically

Theme (music)

In music, a theme is the material, usually a recognizable melody, upon which part or all of a composition is based.-Characteristics:A theme may be perceivable as a complete musical expression in itself, separate from the work in which it is found . In contrast to an idea or motif, a theme is...

 and tonally

Tonality

Tonality is a system of music in which specific hierarchical pitch relationships are based on a key "center", or tonic. The term tonalité originated with Alexandre-Étienne Choron and was borrowed by François-Joseph Fétis in 1840...

 (that is, each section contains distinct and complete themes, and ends with an authentic cadence. The B section is generally in a contrasting, but closely related key

Closely related key

In music, a closely related key is one sharing many common tones with an original key, as opposed to a distantly related key...

, usually the dominant key

Dominant key

The dominant key in a given musical composition is the key whose tonic is a perfect fifth above the tonic of the main key of the piece. Put another way, the key whose tonic is the dominant scale degree in the main key....

 of the first section's tonic

Tonic (music)

In music, the tonic is the first scale degree of the diatonic scale and the tonal center or final resolution tone. The triad formed on the tonic note, the tonic chord, is thus the most significant chord...

 (a perfect fifth

Perfect fifth

In classical music from Western culture, a fifth is a musical interval encompassing five staff positions , and the perfect fifth is a fifth spanning seven semitones, or in meantone, four diatonic semitones and three chromatic semitones...

 above) or the relative

Relative key

In music, relative keys are the major and minor scales that have the same key signatures. A major and minor scale sharing the same key signature are said to be in a relative relationship...

 or parallel

Parallel key

In music, parallel keys are the major and minor scales that have the same tonic. A major and minor scale sharing the same tonic are said to be in a parallel relationship...

 minor or major, less often the subdominant

Subdominant

In music, the subdominant is the technical name for the fourth tonal degree of the diatonic scale. It is so called because it is the same distance "below" the tonic as the dominant is above the tonic - in other words, the tonic is the dominant of the subdominant. It is also the note immediately...

 key (a perfect fifth below). It usually also has a contrasting character; in a march

March (music)

A march, as a musical genre, is a piece of music with a strong regular rhythm which in origin was expressly written for marching to and most frequently performed by a military band. In mood, marches range from the moving death march in Wagner's Götterdämmerung to the brisk military marches of John...

, for example, the highly rhythmic and strident character of the march itself is usually contrasted with a more lyrical and flowing trio in the subdominant, and often in a 3/4

Triple metre

Triple metre is a musical metre characterized by a primary division of 3 beats to the bar, usually indicated by 3 or 9 in the upper figure of the time signature, with 3/4, 3/2, and 3/8 being the most common examples...

 time signature

Time signature

The time signature is a notational convention used in Western musical notation to specify how many beats are in each measure and which note value constitutes one beat....

 as opposed to the 4/4 of the primary march theme.

A distinction is sometimes made between "compound ternary form" – in which each large part of the form is itself divided in a way to suggest ternary or binary form (giving, for example, an overall scheme of – and "simple ternary form", in which each large part of the form has no particular structure itself. Da capo arias

Da capo aria

The da capo aria is a musical form, which was prevalent in the Baroque era. It is sung by a soloist with the accompaniment of instruments, often a small orchestra. The da capo aria is very common in the musical genres of opera and oratorio...

 are usually in simple ternary form; minuets (or scherzos) and trios are normally compound. Another name for the latter is "composite ternary form".

The repetition of any section results in expanded ternary form.

Commonly, the third section will feature more ornamentation than the first section (as is often the case with da capo arias). In these cases the last section is sometimes labeled A’ or A1 to indicate that it is slightly different from the first A section.

Usage

As well as in marches, ternary form is often found in baroque

Baroque music

Baroque music describes a style of Western Classical music approximately extending from 1600 to 1760. This era follows the Renaissance and was followed in turn by the Classical era...

 opera

Opera

Opera is an art form in which singers and musicians perform a dramatic work combining text and musical score, usually in a theatrical setting. Opera incorporates many of the elements of spoken theatre, such as acting, scenery, and costumes and sometimes includes dance...

 aria

Aria

An aria in music was originally any expressive melody, usually, but not always, performed by a singer. The term is now used almost exclusively to describe a self-contained piece for one voice usually with orchestral accompaniment...

s (the da capo aria) and in many dance forms, such as polka

Polka

The polka is a Central European dance and also a genre of dance music familiar throughout Europe and the Americas. It originated in the middle of the 19th century in Bohemia...

s. It is also the form used in the minuet (or scherzo) and trio, which, in the Classical era

Classical period (music)

The dates of the Classical Period in Western music are generally accepted as being between about 1750 and 1830. However, the term classical music is used colloquially to describe a variety of Western musical styles from the ninth century to the present, and especially from the sixteenth or...

, was usually the third movement of symphonies

Symphony

A symphony is an extended musical composition in Western classical music, scored almost always for orchestra. A symphony usually contains at least one movement or episode composed according to the sonata principle...

, string quartet

String quartet

A string quartet is a musical ensemble of four string players – usually two violin players, a violist and a cellist – or a piece written to be performed by such a group...

s, sonata

Sonata

Sonata , in music, literally means a piece played as opposed to a cantata , a piece sung. The term, being vague, naturally evolved through the history of music, designating a variety of forms prior to the Classical era...

s and similar works.