Catalogues of classical compositions

This article gives some details of the various catalogues of classical compositions that have come into general use.

While the opus numbering system has long been the standard manner in which individual compositions are identified and referenced, it is far from universal, and there have been many different applications of the system. Very few composers gave opus numbers to all of their published works without exception:

There are cases where works that a composer chose not to publish were published after their death and assigned very late opus numbers that often give a misleading idea of their order of composition (cases include Mendelssohn, Chopin and Tchaikovsky).

Other composers simply never used opus numbers at all (examples include Copland, Vaughan Williams and many other 20th-century composers).

In some cases, the opus numbers that were established during the composer's lifetime are still used, but symbols from alternative comprehensive catalogues are used for unpublished works or works that have come to light since the composer's death.

For the above and other reasons, musicologists have often found it necessary to produce comprehensive catalogues that incorporate the most up-to-date information available about the composers' works. These catalogues sometimes also include unpublished sketches, incomplete drafts, even doubtful works and those known to have been spuriously attributed, as well as writings and other non-musical output.

When such a catalogue finds general acceptance, the sequence numbers allocated by the author then become the standard way of referencing the composer's works, and these numbers usually supersede the opus numbers (if any) that were previously used.

Some such catalogues are organised in a single chronological sequence; others are divided into different genres and listed chronologically within each genre; others are alphabetically arranged. Thematic catalogue indicates a catalogue with a music example (incipit/theme) for each entry, usually represented on one or two staves. A symbol is chosen to represent the catalogue as a whole, and this is usually the initial of the author's or the composer's surname, or an abbreviation of the title of the catalogue itself. In a small number of cases, different symbols apply to different parts of the catalogue.

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