- Barry S. Brook
A thematic catalogue is an index to a group of musical compositions that incorporates citations of their opening notes (incipits), or principal melodic features (themes), or both. These citations may be given in various forms, such as conventional notes, neumes, tablatures, syllables, numbers, letters or computer codes.
In practice, defying etymology, most thematic catalogues are concerned with incipits rather than with themes. The semantic confusion arose in the late 18th century, when the terms ‘theme’ and ‘thematic catalogue’ were first regularly used. Because compositions almost always began with their main theme, the words ‘theme’ or ‘themata’ were treated as synonymous with what has only recently come to be called ‘incipit’. In the 18th century, they were used interchangeably with ‘initia’, ‘beginnings’, ‘commencements’, ‘Anfänge’, ‘subjects’ or ‘first few bars’. The combined term ‘thematic catalogue’ was first used in print by J.J. Hummel in 1768 for what was really an incipit index (but not the earliest: see §2(i) and (iii) below). In the 20th century, in the relatively few instances where true themes rather than incipits are catalogued, the adjective ‘thematic’ is avoided in the title (e.g. H. Barlow and S. Morgenstern: ...