A thematic catalog (or thematic index) is a list of works, usually of one composer, but occasionally of a specific collection of a specific institution or of multiple composers, based on medium of performance, type of work, etc. Some may include a detailed description of each work. These descriptions may include one or more of the following:
- name of the work
- name by which the work is popularly known
- medium of performance
- form or type of composition
- opus and serial or work number
- author of text, if applicable
- musical incipit (the opening notes (and text, when applicable) of a work, and, in some cases, the opening notes of each movement)
- location of manuscript
- date and/or place of composition
- date and/or place of first and/or subsequent publication
A catalog may be arranged in chronological order by opus or work number or by some other method, for example, by medium of performance. Those arranged by medium of performance may be sub-arranged in chronological order or by key.
An opus number is a unique number assigned by a composer or by publishers to some or all of that composer's work or group of works.
According to New Grove, opus number were, until 1800, more common in instrumental music than in vocal music and stage works. In the seventeenth and eighteenth centuries, opus numbers frequently were assigned by the publisher at the time of publication. It was not uncommon for different publishers to issue the same work under different opus numbers or to assign the same opus number to different works by the same composer. Considering all this, it is not safe to assume that opus numbering represents chronological order.
Opus numbers may appear in Arabic or roman form. The word "opus" may be in another language ("œuvre," "soch.," etc.), may be abbreviated ("op.," "œuv.," etc.), or may be another word meaning with the same meaning ("Werk").
“WoO" is used when most, but not all, of a composer's works have opus numbers. The works that cannot be identified numerically are arranged chronologically or by form or genre and assigned numbers preceded by "WoO." This stands for Werke ohne Opuszahl, or "works without opus numbers." WoO numbers for a composer's works are used in authorized access points for music when they appear in a thematic index, in reference sources, or on published works.
Serial numbers are usually assigned by the composer to a group of work of the same type of composition or in the same form in the order in which the works were written. Serial numbers that have been assigned posthumously are generally not used in authorized access points for music.
Work numbers (or thematic index numbers) are assigned by the person who creates a catalog of a composer's works. A "thematic index" or "thematic catalog" may be arranged chronologically, by medium of performance, by type of composition, or by some other criterion.
Thematic index numbers generally have an alphabetic prefix in the form of an initial or acronym. An initial may be first initial of the compiler's last name. The "K." in Mozart's thematic index number stands for Ludwig Köchel, the organizer of Mozart's works. When the numbers are taken from a reference source other than a thematic index, the first initial of the last name of the author of the article or book may be used. The thematic index numbers for Michel de Lalande are taken from the article by Sawkins in New Grove and are preceded by the letter "S." Two letters may represent the first initials of the composer's first and last names, as is the case with "MH," for Michael Haydn, or multiple authors of the composer's thematic index, such as "BI," standing for Bianchi and Inzaghi's index of Alessandro Rolla's works.
A thematic index number may also be an acronym representing the title of the thematic index. The letters in the thematic index numbers for J. S. Bach's works, "BWV," stand for Bach-Werke-Verzeichnis [Bach Work List], compiled by Wolfgang Schmieder.
Some thematic index numbers include indication of key, such as those for Johann Friedrich Fasch or Georg Philipp Telemann. In the following examples, the "FWV" is taken from the title of the thematic index for Fasch, Verzeichnis der Werke von Johann Friedrich Fasch [List of works by Johann Friedrich Fasch]. The thematic index is divided into sections by type of work/medium of performance, with each section assigned a letter. The letter is given in uppercase in an authorized access point. Section L lists Fasch's concertos. The letter following the colon signifies key, with uppercase letters for major keys and lowercase letters for minor keys. The number following the key indicates the position of that work within the sequence of works in that category and in that key, with numbers assigned by the compiler of the thematic index.
|Thematic index number||Key|
|FWV L:D11||D major|
|FWV L:e1||E minor|
The thematic index numbers for Telemann's instrumental music are from Telemann-Werkverzeichnis, Instrumentalwerke [Telemann work list, instrumental works]. The source is divided into numbered sections. Section 42 includes works for two instruments and continuo, further subdivided by key.
|Thematic index number||Key|
|TWV 42:f1||F minor|
|TWV 42:F5||F major|
Thematic catalogs may be superceded by newer catalogs. For example, the harpsichord sonatas of Domenico Scarlatti are currently assigned "K." numbers, for Ralph Kirkpatrick's ordering of the sonatas. Previously, "L." numbers, for Alessandro Longo's organization of the sonatas, were used. Generally, when a new thematic catalog is issued, it includes a concordance referring the new numbers to the numbers used in the older catalog.
When no thematic index exists for a composer, and some or all the works of that composer have been published in a monographic series, the numbering system by which the works have been organized in that source may be used. Work numbers for several early British composers, such as John Bull, William Byrd, Orlando Gibbons, and John Ward, are taken from the series Musica Britannica. Work numbers for these composers are preceded by "MB." The number in this authorized access point for a work by John Bull is taken from Musica Britannica volume 14, which is Bull's keyboard music. The work is number 25 in that volume:
Bull, John, -1628. In nomines, keyboard instrument, MB 25, A minor
See also Work numbers for authorized access points for composers whose works are assigned numbers other than opus numbers or in addition to opus numbers.
Koth, Michelle. Uniform titles for music. Lanham, Md: Scarecrow Press, 2008.
Classical music cataloging systems explained
Thematic catalog (index) in The Harvard dictionary of music