, from the Latin
meaning "work", is usually used in the sense of "a work of art
". In this sense the plural of opus, "opera
", is used to refer to the genre of music drama.
Since about the 17th century, many composers, such as Ludwig van Beethoven, have identified their musical works by opus numbers. This is abbreviated "Op."; the plural is "Opp." Throughout the nineteenth century, these were normally assigned by publishers who published groups of like works together, usually in sets of 3, 6, or 12. They consequently often have little relationship to chronological order of composition, even when this may be determined. Those works that did not happen to get published at the time lack opus numbers. Also, gaps and duplications in the numbering sequences, especially when multiple publishers are involved, are frequent. Some examples of this are discussed below under individual composers.
Many opus numbers, such as those of Mozart and Bach, are so useless and so adequately replaced by catalogs that they are no longer used to identify the works at all. The multiple-set opus numbers best-known today are those of the string quartets of Joseph Haydn. Haydn's Op. 76, for instance, consists of six quartets, known individually as Op. 76 No. 1, etc., while his Op. 74 consists of three quartets, similarly identified.
19th Century and modern era
Starting about 1800, especially with the works of Beethoven, opus numbers tended to be assigned by the composer. These were usually applied to individual works, though later composers often continued to assign opus numbers to sets, especially of short piano pieces and songs. Gradually the connection between opus number and publication has been lost, and many composers since 1900 have given opus numbers to works that are not necessarily published at all. Consequently opus numbers, when present, are a better guide to chronology of composition, though they are not always reliable.
Beethoven was very selective in his early years about which works he assigned opus numbers to, omitting numbers even on some works he sent for publication. Many in this category have since his death been assigned numbers labeled "WoO", standing for "Werk ohne Opuszahl" or "work without an opus number." However, in later years he published some very early works with higher opus numbers, and some works published posthumously were also given opus numbers.
The practice of posthumous opus numbers, sometimes but not always labeled "Op. posth.", is most striking in the case of Felix Mendelssohn. Subsequent to his death, many works were published by his heirs with opus numbers. For example, Mendelssohn published in his lifetime three symphonies, numbers 1-3, with the opus numbers 11, 52, and 56. Two symphonies composed between No. 1 and No. 2, but withdrawn by the composer, the "Italian" and the "Reformation", were published after his death and called No. 4 and No. 5 respectively, with the opus numbers 90 and 107.
Some composers, such as Cesar Franck and Béla Bartók, used opus numbers early in their careers but soon dropped them. Others, such as Carl Nielsen and Paul Hindemith, used them inconsistently. Yet others have been strict and conscientious, most notably Sergei Prokofiev. He habitually assigned opus numbers to works before beginning to compose them, leaving some fragmentary or planned works with opus numbers on his death. He even assigned new opus numbers to revised works; thus his Symphony No. 4 is both Op. 47 and Op. 112, and his Piano Sonata No. 5 is both Op. 38 and Op. 135, depending on the edition.
Because of the problems of using opus numbers to identify works particularly for composers from the baroque and classical eras, and the absence and scattered use of opus numbers by composers of all eras, many composers' works have been definitely catalogued by individual scholars, and in such cases their works may be unambiguously referred to by their thematic catalog abbreviations.
Individual examples of usage
- The works of Carl Friedrich Abel, while usually referenced by their original publication opus numbers (for example, his Op. 17 symphonies), also have catalog numbers assigned to them by Walter Knape in his Bibliographisch-thematisches Verzeichnis der Kompositionen von Karl Friedrich Abel (Cuxhaven: W. Knape, 1972).
- Carl Philipp Emanuel Bach's works have two numbering systems: the older Wotquenne numbering (abbreviated as Wq.) devised by Alfred Wotquenne in his catalog of Emanuel's music published in 1905, and the more complete and up-to-date numbering by E. Eugene Helm (abbreviated as H.), as presented in Helm's Thematic Catalogue of the Works of C.P.E. Bach (New Haven: Yale University Press, 1989).
- Johann Christian Bach's works are most often referred to by the opus numbers assigned by their original publishers, which can cause identification difficulties because different publishers used the same opus number. (For instance, "Op. 18" was used for three different sets of J.C. Bach works: "Six Grand Overtures," "Deux sinfonies," and "Four Sonatas and Two Duets," and three of his six Op. 6 symphonies also appear in his Op. 8 in a different order.) Because of this, some have used C.S. Terry's John Christian Bach (2nd edition; London: Oxford University Press, 1967) as the basis for a de facto standard, using the page number and incipit number in Terry for identification even though these numbers were not assigned by Terry for cataloguing purposes. (For a convenient short listing of these numbers, see Christoph Wolff, et al., The New Grove Bach Family [NY: Norton, 1983], pp. 341ff..) Numbers are also sometimes used from the Thematic Catalog in the Collected Works of Johann Christian Bach (gen. ed. Ernest Warburton; NY: Garland Publishing, 1985).
- Johann Sebastian Bach's works are referred to by their BWV or Bach-Werke-Verzeichnis numbers after the catalogue by Wolfgang Schmieder.
- Wilhelm Friedemann Bach's works were catalogued by Martin Falck in 1913, and are often referred to by their F (or Falck) numbers.
- Béla Bartók's works are designated by numbering systems developed by three different catalogers. The most frequently-used is the chronological "Sz." system created by András Szöllősy.
- Dietrich Buxtehude's works are referred to by their Buxtehude-Werke-Verzeichnis numbers, abbreviated BuxWV, after the catalogue published by Georg Karstädt.
- Marc Antoine Charpentier's works are referred to by the H or Hitchcock numbers after Hugh Wiley Hitchcock.
- Antonín Dvořák's works are usually now referenced by B numbers, after Jarmil Burghauser's comprehensive catalogue which resolved a great many difficulties with the often misleading and duplicated opus numbers given by different publishers to Dvořák's works
- George Frideric Handel's works are often designated by HWV (Händel-Werke-Verzeichnis) numbers as given in the Verzeichnis der Werke Georg Friedrich Händels by Bernd Baselt. (See this page at gfhandel.org for additional details.)
- Joseph Haydn's works are referred to by their Hob or Hoboken numbers after Anthony van Hoboken's 1957 classification. Hoboken assigned numbers to the string quartets, but these are generally still known by their opus numbers.
- Franz Liszt's works are referred to by their S or Searle numbers after Humphrey Searle's 1960s classification The Music of Liszt. Alternately, R is used to refer to Peter Raabe's 1931 reference Franz Liszt: Leben und Schaffen.
- Wolfgang Amadeus Mozart's opus numbers are particularly scattered and useless and are no longer used at all (for instance, there are two sets of violin sonatas both called Op. 1). His works are always referred to by their K or Köchel numbers, after Ludwig von Köchel. In continental Europe, the German abbreviation "KV" for Köchel-Verzeichnis is more common; see that entry for an explanation of the differing K numbers found between the first and subsequent editions of Köchel's catalog. See also: List of compositions by Wolfgang Amadeus Mozart
- Antonio Rosetti's works are usually given with catalog numbers by Sterling E. Murray, Chairman of the Department of Music History at West Chester University of Pennsylvania, although older numbers from Oskar Kaul's 1912 Rosetti catalog sometimes appear as well. For example, Rosetti's popular "La Chasse" symphony is numbered as "Murray A20/Kaul I:18."
- Domenico Scarlatti's harpsichord works have two major numbering systems: the L or Longo numbers after Alessandro Longo's edition for piano, and the K or Kirkpatrick numbers after Ralph Kirkpatrick's facsimile edition (K is sometimes written as Kk to distinguish it from Köchel numbers - see Mozart above). A newer ordering, by Giorgio Pestelli, has led to P numbers appearing in some places.
- Franz Schubert's works are referred to by their D or Deutsch numbers after Otto Erich Deutsch's catalogue. Schubert's opus numbers are very scattered, unchronological, and mostly posthumous, but a few of them are occasionally seen.
- Antonio Soler's keyboard sonatas are usually referred to by their R number, after the catalogue compiled by Father Samuel Rubio.
- Antonio Vivaldi's works are referred to by their RV or Ryom-Verzeichnis numbers after Peter Ryom's catalogue. Some of his works were published in opus sets, and these numbers are often still used as well.
- Richard Wagner's works are referred to by their WWV or Wagner-Werke-Verzeichnis numbers, which also include his non-musical work.
- Carl Maria von Weber's works may appear by opus or by J. number, the latter referring to Friedrich Wilhelm Jähns, Carl Maria von Weber in Seinen Werken: Chronologisch-Thematisches Verzeichnis Seiner Sämmtlichen Compositionen (1871). A list of Weber's works in order of Jähns catalogue number can be found at List of compositions by Carl Maria von Weber.
- In a parody of this, the works of P. D. Q. Bach are assigned "Schickele" numbers, after Peter Schickele, the works' sole discoverer (and, in reality, their composer). Schickele numbers are not sequential but are intended as jokes (a Christmas work is S.359 because 25 December is the 359th day of the (non-leap) year.