Binary form is a 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...

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

Dance

Dance is an art form that generally refers to movement of the body, usually rhythmic and to music, used as a form of expression, social interaction or presented in a spiritual or performance setting....

.

Binary form was popular in the Baroque period

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...

, often used to structure movements of keyboard

Keyboard instrument

A keyboard instrument is a musical instrument which is played using a musical keyboard. The most common of these is the piano. Other widely used keyboard instruments include organs of various types as well as other mechanical, electromechanical and electronic instruments...

 sonatas. It was also used for short, one-movement works. Around the middle of the 18th century, the form largely fell from use as the principal design of entire movements as sonata form

Sonata form

Sonata form is a large-scale musical structure used widely since the middle of the 18th century . While it is typically used in the first movement of multi-movement pieces, it is sometimes used in subsequent movements as well—particularly the final movement...

 and organic development

Musical development

In European classical music, musical development is a process by which a musical idea is communicated in the course of a composition. It refers to the transformation and restatement of initial material, and is often contrasted with musical variation, which is a slightly different means to the same...

 gained prominence. When it is found in later works, it usually takes the form of the theme in a set of variations, or the 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...

, Scherzo

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...

, or Trio sections of a Minuet and Trio or Scherzo and Trio movement in a sonata, symphony, etc. Many larger forms incorporate binary structures, and many more complicated forms (such as sonata forms) share certain characteristics with binary form.

Structure

Most strictly, a piece in binary form is characterized by two complementary, related sections of roughly equal duration, which come up frequently. The first section will start in a certain key

Key (music)

In music theory, the term key is used in many different and sometimes contradictory ways. A common use is to speak of music as being "in" a specific key, such as in the key of C major or in the key of F-sharp. Sometimes the terms "major" or "minor" are appended, as in the key of A minor or in the...

, and will usually modulate

Modulation (music)

In music, modulation is most commonly the act or process of changing from one key to another. This may or may not be accompanied by a change in key signature. Modulations articulate or create the structure or form of many pieces, as well as add interest...

 to a 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...

:

• compositions in major keys will typically modulate to the dominant
  Dominant (music)
  In music, the dominant is the fifth scale degree of the diatonic scale, called "dominant" because it is next in importance to the tonic,and a dominant chord is any chord built upon that pitch, using the notes of the same diatonic scale...
  
  , the fifth scale degree above the 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...
  
  
• compositions in minor keys will typically modulate to the relative major
  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...
  
  , the major key centered on the third scale degree above the tonic; alternatively the first section could close in the dominant minor, or with an imperfect cadence
  Cadence (music)
  In Western musical theory, a cadence is, "a melodic or harmonic configuration that creates a sense of repose or resolution [finality or pause]." A harmonic cadence is a progression of two chords that concludes a phrase, section, or piece of music...
  
   in the original key.

The second section of the piece begins in the newly established key, where it remains for an indefinite period of time. After some harmonic activity, the piece will eventually modulate back to its original key before ending. More often than not, especially in 18th-century compositions, the A and B sections are separated by double bars

Bar (music)

In musical notation, a bar is a segment of time defined by a given number of beats of a given duration. Typically, a piece consists of several bars of the same length, and in modern musical notation the number of beats in each bar is specified at the beginning of the score by the top number of a...

 with repeat signs, meaning both sections were to be repeated.

Binary form is usually characterised as having the form AB, though since both sections repeat, a more accurate description would be AABB. Others, however, prefer to use the label AA′. This second designation points to the fact that there is no great change in character between the two sections. The rhythm

Rhythm

Rhythm may be generally defined as a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions." This general meaning of regular recurrence or pattern in time may be applied to a wide variety of cyclical natural phenomena having a periodicity or...

s and melodic

Melody

A melody , also tune, voice, or line, is a linear succession of musical tones which is perceived as a single entity...

 material used will generally be closely related in each section, and if the piece is written for a musical ensemble

Musical ensemble

A musical ensemble is a group of people who perform instrumental or vocal music. In classical music, trios or quartets either blend the sounds of musical instrument families or group together instruments from the same instrument family, such as string ensembles or wind ensembles...

, the instrumentation

Instrumentation (music)

In music, instrumentation refers to the particular combination of musical instruments employed in a composition, and to the properties of those instruments individually...

 will generally be the same. This is in contrast to the use of verse-chorus form

Verse-chorus form

Verse-chorus form is a musical form common in popular music and predominant in rock since the 1960s. In contrast to AABA form, which is focused on the verse , in verse-chorus form the chorus is highlighted...

 in popular music

Popular music

Popular music belongs to any of a number of musical genres "having wide appeal" and is typically distributed to large audiences through the music industry. It stands in contrast to both art music and traditional music, which are typically disseminated academically or orally to smaller, local...

—the contrast between the two sections is primarily one of the keys used.

Further distinctions

A piece in binary form can be further classified according to a number of characteristics:

Simple vs. rounded

Occasionally, the B section will end with a "return" of the opening material from the A section. This is referred to as rounded binary, and is labeled as ABA′. In rounded binary, the beginning of the B section is sometimes referred to as the "bridge", and will usually conclude with a half cadence

Cadence (music)

In Western musical theory, a cadence is, "a melodic or harmonic configuration that creates a sense of repose or resolution [finality or pause]." A harmonic cadence is a progression of two chords that concludes a phrase, section, or piece of music...

 in the original key. Rounded binary is not to be confused with ternary form

Ternary form

Ternary form, sometimes called song form, is a three-part musical form, usually schematicized as A-B-A. The first and third parts are musically identical, or very nearly so, while the second part in some way provides a contrast with them...

, also labeled ABA—the difference being that, in ternary form, the B section contrasts completely with the A material as in, for example, a minuet and trio

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...

. Another important difference between the rounded and ternary form is that in rounded binary, when the "A" section returns, it will typically contain only half of the full "A" period, whereas ternary form will end with the full "A" section.

Rounded binary or minuet form:
A :||: B A or A'
I(->V) :||: V(or other closely related

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...

) I

If the B section lacks such a return of the opening A material, the piece is said to be in simple binary.

Simple:
A->B :||: A->B
I->V :||: V->I

Slow-movement form:
A' A"
I->V I->I

Sectional vs. continuous

If the A section ends with an Authentic (or Perfect) cadence

Cadence (music)

In Western musical theory, a cadence is, "a melodic or harmonic configuration that creates a sense of repose or resolution [finality or pause]." A harmonic cadence is a progression of two chords that concludes a phrase, section, or piece of music...

 in the original 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...

 key of the piece, the design is referred to as a sectional binary. This refers to the fact that the piece is in different tonal sections, each beginning and ending in their own respective keys.

If the A section ends with any other kind of cadence, the design is referred to as a continuous binary. This refers to the fact that the B section will "continue on" with the new key established by the cadence at the end of A.

Symmetrical vs. asymmetrical

If the A and B sections are roughly equal in length, the design is referred to as symmetrical.

If the A and B sections are of unequal length, the design is referred to as asymmetrical. In such cases, the B section is usually substantially longer than the A section.

The asymmetrical binary form begins to be more common than the symmetrical type from about the time of Beethoven onwards, and is almost routine in the main sections of Minuet and Trio or Scherzo and Trio movements in the works of many composers from Beethoven onwards. In such cases, occasionally only the first section of the binary structure is marked to be repeated.

Although most of Chopin's nocturnes are in an overall ternary form

Ternary form

Ternary form, sometimes called song form, is a three-part musical form, usually schematicized as A-B-A. The first and third parts are musically identical, or very nearly so, while the second part in some way provides a contrast with them...

, quite often the individual sections (either the A, the B, or both) are in binary form, most often of the asymmetrical variety. If a section of this binary structure is repeated, in this case it is written out again in full, usually considerably varied, rather than enclosed between repeat signs.

Balanced binary

In some simple continuous binary forms, there is a kind of "rhyme" between the closing gesture of the first reprise and the closing gesture of the second. In other words, the cadential material at the end of the first reprise (in the key of the dominant) will return, transposed to the tonic, at the end of the second reprise. This is referred to as balanced binary.