(Lat.: ‘work’; Fr. oeuvre; Ger. Opus; It. opera).
The Latin plural, opera, has become singular in Italian, and its plural is opere. To avoid confusion with the usual English or Italian meaning of ‘opera’, the English plural, ‘opuses’, may be preferred. First used for a musical composition in the Renaissance (Tinctoris, prologue to Liber de arte contrapuncti, 1477; Listenius, Musica, 1537), ‘opus’ was applied by early German publishers to whole collections: Novum et insigne opus musicum (1537–8) and Magnum opus musicum (1604). One of the earliest instances of a single-composer publication with opus number was Viadana’s Motecta festorum op.10 (Venice, 1597). Biagio Marini published 22 numbered sets in Venice and other cities from 1617 to 1655. Until 1800 opus numbers were more common in instrumental than in vocal music, and they have rarely been applied to stage compositions at any period.
In the absence of corroborating information, opus numbers can never be relied upon to establish the chronology of a composer’s works. Generally, numbers were not applied until publication, and then often by the publisher, not the composer. Where the same work appears with two publishers, it may have different numbers assigned to it (as with Haydn, or with Boccherini, who assigned further numbers in his own catalogue). Sometimes, as in the case of Schütz, the numbers were added later. Before about 1800 it was customary for several works to be gathered under one number, often 12 in the early 18th century, later six and then, as individual works became longer (towards 1800), three or two; the chronology may not correspond with the internal numbering (it does not in Beethoven’s op.18 quartets for example). Smaller pieces, occasional compositions, youthful works and works in manuscript are not usually numbered, and miscellaneous clues must be used to fit them into the list of numbered works.
DAVID FULLER