Opus

One work, one number

The word comes from Latin and means “work”. Since the 17th century composers and publishers have numbered publications so that they can be told apart. The number therefore says first of all only when a work appeared, and not necessarily when it was composed. Early works printed late carry a high opus number, and works that appeared only after the composer's death are often marked “op. posth.”, that is, posthumous.

When the opus number is missing

Not every piece has an opus number. Small works, unprinted pieces and occasional works often stay without one. For these, researchers have compiled catalogues that number every work of a composer. For Beethoven the pieces without opus number are gathered as “WoO”, for Bach the Bach Works Catalogue (BWV) applies, for Schubert the catalogue by Otto Erich Deutsch (D.), for Mozart that by Köchel (K.). The addition “Anh.” points to the appendix of a catalogue in which pieces of uncertain attribution are listed. The minuet from the Notebook for Anna Magdalena Bach, for example, which the archive lists as “BWV Anh. 114”, names in the version of the sheet music collection Christian Petzold as composer and not Bach himself.

Same opus number, different composers

• Etüde Nr. 7 Matteo Carcassi, op. 60 No. 7 · guitar · 2 pages

  The archive lists the étude as op. 60 No. 7 by Carcassi.

• Lektion Nr. 5 Fernando Sor, op. 60 No. 5 · guitar · 1 page

  Sor's lessons too run under op. 60. The same opus number for two composers is no contradiction, since each composer counts for himself.

Without opus number

• Für Elise Ludwig van Beethoven, WoO 59 · piano · 3 pages

  One of the best-known piano pieces carries no opus number but the number 59 in the catalogue of works without opus number.

A cycle under one opus number

• Armes Waisenkind Robert Schumann, op. 68 No. 6 · piano · 1 page

  Opus 68 is a whole collection of small piano pieces. The number after the opus number denotes the single piece in the cycle.

Counting and searching

In practice the opus number helps with finding: anyone looking for a title such as “Sonata” or “Étude” needs the number to hit the right edition. Two pitfalls are to be noted. First, every composer counts for himself, so the number alone is never enough. Second, with collections the opus number is given for the whole volume and the pieces in it are counted separately, as with Schumann's op. 68 and Grieg's op. 46.

Common mistakes

• Reading the opus number as a date of composition: it counts publication.
• Confusing two composers with the same opus number: Carcassi and Sor both have an op. 60.
• Taking “Anh.” for a number: it denotes the appendix of a catalogue.