In musical notation

Musical notation

Music notation or musical notation is any system that represents aurally perceived music, through the use of written symbols.-History:...

, a bar (or measure) is a segment of time defined by a given number of beats

Beat (music)

The beat is the basic unit of time in music, the pulse of the mensural level . In popular use, the beat can refer to a variety of related concepts including: tempo, meter, rhythm and groove...

 of a given duration. Typically, a piece consists of several bars of the same length, and in modern musical notation

Modern musical symbols

Modern musical symbols are the marks and symbols that are widely used in musical scores of all styles and instruments today. This is intended to be a comprehensive guide to the various symbols encountered in modern musical notation.- Lines :- Clefs :...

 the number of beats in each bar is specified at the beginning of the score by the top number of a 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....

 (such as 3/4).

The word bar is more common in British English

British English

British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

, while the word measure is more common in American English

American English

American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

, although musicians generally understand both usages. In American English, although the words bar and measure are often used interchangeably the correct use of the word 'bar' refers only to the vertical line itself, while the word 'measure' refers to the beats contained between bars. In international usage, it is equally correct to speak of bar numbers and measure numbers, e.g. ‘bars 9–16’ or ‘mm. 9–16’. Along the same lines, it is wise to reserve the abbreviated form ‘bb. 3–4’ etc. for beats only; bars should be referred to by name in full.

The first metrically complete measure within a piece of music is called ‘bar 1’ or ‘m. 1’. When the piece begins with an upbeat (an incomplete measure at the head of a piece of music), ‘bar 1’ or ‘m. 1’ is the following measure.

Bar

Originally, the word bar derives from the vertical lines drawn through the staff to mark off metrical units and not the bar-like (i.e., rectangular) dimensions of a typical measure of music. In British English, these vertical lines are called bar, too, but often the term bar-line is used in order to make the distinction clear. In American English, the word bar stands for the lines and nothing else. A double bar-line (or double bar) can consist of two single bar-lines drawn close together, separating two sections

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...

 within a piece, or a bar-line followed by a thicker bar-line, indicating the end of a piece or movement. Note that the term double bar refers not to a type of bar (i.e., measure), but to a type of bar-line. Another term for the bar-line denoting the end of a piece of music is music end.

A repeat sign (or, repeat bar-line) looks like the music end, but it has two dots, one above the other, indicating that the section of music that is before is to be repeated. The beginning of the repeated passage can be marked by a begin-repeat sign; if this is absent the repeat is understood to be from the beginning of the piece or movement. This begin-repeat sign, if appearing at the beginning of a staff, does not act as a bar-line because no bar is before it; its only function is to indicate the beginning of the passage to be repeated.

In music with a regular meter

Metre (music)

Meter or metre is a term that music has inherited from the rhythmic element of poetry where it means the number of lines in a verse, the number of syllables in each line and the arrangement of those syllables as long or short, accented or unaccented...

, bars function to indicate a periodic agogic accent in the music, regardless of its duration. In music employing mixed meters

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....

, bar-lines are instead used to indicate the beginning of rhythmic note groups, but this is subject to wide variation: some composers use dashed bar-lines, others (including Hugo Distler

Hugo Distler

Hugo Distler was a German organist, choral conductor, teacher and composer.-Life and career:...

) have placed bar-lines at different places in the different parts to indicate varied groupings from part to part.
Bars and bar-lines also indicate grouping: 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...

ically of beats within and between bars, within and between phrases

Phrase (music)

In music and music theory, phrase and phrasing are concepts and practices related to grouping consecutive melodic notes, both in their composition and performance...

, and on higher levels such as meter.

Hypermeasure

A hypermeasure, large-scale or high-level measure, or measure-group is a metric unit

Meter (music)

Meter or metre is a term that music has inherited from the rhythmic element of poetry where it means the number of lines in a verse, the number of syllables in each line and the arrangement of those syllables as long or short, accented or unaccented...

 in which, generally, each regular measure is one beat (actually hyperbeat) of a larger meter. Thus a beat is to a measure as a measure/hyperbeat is to a hypermeasure. Hypermeasures must be larger than a notated bar, perceived as a unit, consist of a pattern of strong and weak beats, and along with adjacent hypermeasures, which must be of the same length, create a sense of hypermeter. The term was coined by Edward T. Cone

Edward T. Cone

Edward Toner Cone was an American composer, music theorist, pianist, and philanthropist.Cone studied composition under Roger Sessions at Princeton University, receiving his bachelor's in 1939...

in Musical Form and Musical Performance (New York: Norton, 1968).

Further reading

• Cone, Edward T. (1968). Musical Form and Musical Performance. ISBN 0393097676.