In music, the opus number is the "work number" that is assigned to a musical composition, or to a set of compositions, to indicate the chronological order of the composer's publication of that work.
Opus numbers are used to distinguish among compositions with similar titles; the word is abbreviated as "Op."
Given composers' inconsistent or non-existent assignment of opus numbers, especially during the Baroque (1600–1750) and the Classical (1750–1827) eras, musicologists have developed other catalogue-number systems; among them the Bach-Werke-Verzeichnis (BWV-number) and the Köchel-Verzeichnis (K- and KV-numbers), which enumerate the works of Johann Sebastian Bach and Wolfgang Amadeus Mozart, respectively.
[2] In compositional practice, numbering musical works in chronological order dates from 17th-century Italy, especially Venice.
[4] As a result, the plural opera of opus tends to be avoided in English.
In the arts, an opus number usually denotes a work of musical composition, a practice and usage established in the seventeenth century when composers identified their works with an opus number.
Consequently, opus numbers are not usually in chronological order, unpublished compositions usually had no opus number, and numeration gaps and sequential duplications occurred when publishers issued contemporaneous editions of a composer's works, as in the sets of string quartets by Joseph Haydn (1732–1809) and Ludwig van Beethoven (1770–1827); Haydn's Op.
After approximately 1900, they tended to assign an opus number to a composition whether published or not.
Since his death in 1827, the un-numbered compositions have been cataloged and labeled with the German acronym WoO (Werk ohne Opuszahl), meaning "work without opus number"; the same has been done with other composers who used opus numbers.
1 and 2, which he withdrew for personal and compositional reasons; nevertheless, the Mendelssohn heirs published (and cataloged) them as the Italian Symphony No.
To achieve better sales, some publishers, such as N. Simrock, preferred to present less experienced composers as being well established, by giving some relatively early works much higher opus numbers than their chronological order would merit.
In other cases, Dvořák gave lower opus numbers to new works to be able to sell them to other publishers outside his contract obligations.
Other examples of composers' historically inconsistent opus-number usages include the cases of César Franck (1822–1890), Béla Bartók (1881–1945), and Alban Berg (1885–1935), who initially numbered, but then stopped numbering their compositions.
Likewise, depending upon the edition, the original version of Piano Sonata No.
Despite being used in more or less normal fashion by a number of important early-twentieth-century composers, including Arnold Schoenberg (1874–1951) and Anton Webern (1883–1945), opus numbers became less common in the later part of the twentieth century.
To manage inconsistent opus-number usages – especially by composers of the Baroque (1600–1750) and of the Classical (1720–1830) music eras – musicologists have developed comprehensive and unambiguous catalogue number-systems for the works of composers such as: