Editing Opus number (section)

==19th century to date==
From about 1800, composers usually assigned an opus number to a work or set of works upon publication. After approximately 1900, they tended to assign an opus number to a composition whether published or not. However, practices were not always perfectly consistent or logical. For example, early in his career, Beethoven selectively numbered his compositions (some published without opus numbers), yet in later years, he published early works with high opus numbers. Likewise, some posthumously published works were given high opus numbers by publishers, even though some of them were written early in Beethoven's career. 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. (There are also other catalogs of Beethoven's works&nbsp;– see [[Catalogues of Beethoven compositions]].)

The practice of enumerating a posthumous opus ("Op. posth.") is noteworthy in the case of [[Felix Mendelssohn]] (1809–47); after his death, the heirs published many compositions with opus numbers that Mendelssohn did not assign. In life, he published two [[symphony|symphonies]] ([[Symphony No. 1 (Mendelssohn)|Symphony No. 1 in C minor, Op. 11]]; and [[Symphony No. 3 (Mendelssohn)|Symphony No. 3 in A minor, Op. 56]]), furthermore he published his symphony-cantata ''[[Lobgesang]]'', Op. 52, which was posthumously counted as his Symphony No. 2; yet, he chronologically wrote symphonies between symphonies Nos. 1 and 2, which he withdrew for personal and compositional reasons; nevertheless, the Mendelssohn heirs published (and cataloged) them as the [[Symphony No. 4 (Mendelssohn)|'' Italian'' Symphony No. 4 in A major, Op. 90]], and as the [[Symphony No. 5 (Mendelssohn)|'' Reformation'' Symphony No. 5 in D major and D minor, Op. 107]].

While many of the works of [[Antonín Dvořák]] (1841–1904) were given opus numbers, these did not always bear a logical relationship to the order in which the works were written or published. 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. This way it could happen that the same opus number was given to more than one of his works.  Opus number 12, for example, was assigned, successively, to five different works (an opera, a [[concert overture]], a string quartet, and two unrelated piano works). In other cases, the same work was given as many as three different opus numbers by different publishers. The sequential numbering of his symphonies has also been confused: (a) they were initially numbered by order of publication, not composition; (b) the first four symphonies to be composed were published after the last five; and (c) the last five symphonies were not published in order of composition. The ''[[New World Symphony]]'' originally was published as No. 5, later was known as No. 8, and definitively was renumbered as No. 9 in the critical editions published in the 1950s.

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. [[Carl Nielsen]] (1865–1931) and [[Paul Hindemith]] (1895–1963) were also inconsistent in their approaches. [[Sergei Prokofiev]] (1891–1953) was consistent and assigned an opus number to a composition ''before'' composing it; at his death, he left fragmentary and planned, but numbered, works. In revising a composition, Prokofiev occasionally assigned a new opus number to the revision; thus [[Symphony No. 4 (Prokofiev)|Symphony No. 4]] is two thematically related but discrete works: Symphony No. 4, Op. 47, written in 1929; and Symphony No. 4, Op. 112, a large-scale revision written in 1947. Likewise, depending upon the edition, the original version of Piano Sonata No. 5 in C major, is cataloged both as Op. 38 and as Op. 135.

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.