Determining the correct uniform title for many of Bach's works can be tricky. Following are a few preliminary hints about his music:
Languages: Few of Bach's works were published in his lifetime, but his surviving manuscripts show that he used a variety of languages for titles. But his native tongue was German, so in general the German-language version of his descriptive titles is used for uniform titles, unless a form title is more appropriate.
Do not worry if you are unfamiliar with the German language. Cross references are used generously in the catalog to lead you from well-known English versions of titles to their German-language equivalents.
Principal vocal forms used by Bach:
Generally, "Masses" and "Magnificat" (singular form) are used as form titles. Other vocal works are most often identified by German-language distinctive titles.
Principal instrumental forms used by Bach:
Many of the instrumental works are filed by form name ("Concertos," "Trio sonatas," etc.). But some--particularly the larger multi-part instrumental works--use the German-language versions of well-known descriptive titles, such as for the organ collection of chorale settings Orgelbuchlein (Little organ book), or the collection of six Franzosische Suiten (French suites) for harpsichord.
Numberings: Each work by Bach is identified by a BWV number. "BWV" is the abbreviation for "Bach-Werk-Verzeichnis" ("Catalog of Bach's works" in English), which is the short-title for the thematic catalog of Bach's works. In some sources, "BWV" is replaced by "S" (for "Schmieder," the name of the man who compiled the catalog), but BWV is the preferred designation for the numberings used in uniform titles.
If you do not know the BWV number for the work you want, you can
find it in most lists of Bach's works, such as the one in the
"Bach" entry in the New Grove dictionary of music
and musicians, or in the Schmieder thematic catalog itself,
which is found in the reference collection. A librarian can help
you locate these sources, and show you how to use them.