Library of Congress Classification

By the end of the 19th century the explosion of printed information and the concomitant growth of library collections generated various book classification systems designed to organize and control library materials. Librarians at the Library of Congress in Washington, our de facto national library, realized that the Library's likely growth required its own new classification system, which was developed (mostly) between 1898 and the 1920s, superseding that devised by Thomas Jefferson and subsequently much modified.

Their system, which took over some of the best features of the Cutter Expansive Classification then in use at Wesleyan, was a practical shelf arrangement for an essentially closed-stack library rather than a theoretical organization of knowledge. (Hence it is weak in medicine and agriculture because of the other national libraries in those subjects.) Today, the L.C. system is used to organize collections in most American academic and research libraries. Wesleyan has used it to classify all new materials since the late 1960s, and the bulk of our earlier collection has been reclassified into L.C. as well. To view a summary outline of the system's class letters and subjects, click here.

The Library of Congress classification consists of thirty separate schedules, each developed by subject specialists at L.C. An organic system, it is revised and corrected daily as new materials have to be classified for the Library's collections. No use is made of synthesis or mnemonics, as in the earlier systems developed by Charles Cutter or Melvil Dewey. Each of the thirty subject schedules has its own structure, notation, auxiliary tables, and index. Where geographical, historical, or form subdivisions are necessary, they are specially developed for each subject without regard to similar subdivisions in the same or in other classes.

The notation is mixed, consisting of one or two letters for main classes followed by ordinal numbers up to a maximum of four digits for subdivisions. Gaps are left between numbers for future expansion, but where these have been filled, decimal subdivision is used. Beyond decimal subdivision, further subdivision of a subject is alphabetical, often by the English name of a subject expressed by "Cutter numbers" (a letter plus one or more digits); this feature results in dispersal of closely related subjects. The works of individual literary figures are organized by various tables, depending on how prolific the author's output.

More information than you probably want to know about the Library of Congress classification system may be found in theEncyclopedia of Library and Information Science(Ref. Z1006.E47, volume 15, pages 93-200 and especially pages 150 to 163).