One of the earliest systems of classification used in the United States was Thomas Jefferson's adaptation of Sir Francis Bacon's system, which organized knowledge into three large divisions: history, poetry, and philosophy. Jefferson sold his library to the United States to replace the Library of Congress's collection which was destroyed by fire during the War of 1812. The Library of Congress continued using Jefferson's system, with modifications, until 1897, when the Library of Congress developed its own system to classify its collection of 1.5 million items.  

Since libraries have traditionally served as repositories of knowledge, a means of accessing this knowledge has always been a necessity. Today, computers make access relatively easy and a bit less reliant on classification, but subject cataloging still plays an important role in how we arrange and locate materials in a library. Even if all knowledge could be captured in machine-readable form, some means of classification would still be necessary. Today's  computerized periodical databases still rely on subject classification as a means of organizing a search for materials. If a searcher relied solely on key words, narrowing a topic would become very time-consuming.  

Classification systems make arranging materials on library shelves easier and likewise make locating materials on library shelves easier. Most systems of classification are based on subject categories and typically move from the general to the specific in their organization. Library of Congress (LC) classification, for example, uses general categories for the major areas of knowledge, such as Languages and Literature, Social Sciences, Physical Sciences, etc., breaks those areas into more specific areas of knowledge, such as English Literature or American Literature, further subdivides more specific areas into even more specific divisions, such as Nineteenth Century American Literature, and even categorizes materials by type, such as handbooks, dictionaries, encyclopedias, etc. The classification for American Literature, for example, breaks down into numerous subdivisions. A partial classification for one of its subdivisions follows:  
 

The ultimate goal of classification is ease of access. If all knowledge could be computerized, classification might seem less necessary, but even the smallest computer database relies on indexes to retrieve data. Imagine a database of billions of ideas (which a university library would have in its collections) with only an index of individual words. Without a more clearly delineated system of organization a single search of the word history, for example, might retrieve millions of occurrences. Clearly a subject arrangement makes locating materials easier even on a computer.  

LC Classification. The LC system provides very specific subject arrangement of all materials recording human knowledge. It not only classifies knowledge by subject, it also classifies it by form, that is book, periodical, videotape, recording, etc. The Library of Congress provides guides to each of the letter classifications online.

The basics for arrangement are letters of the alphabet and Arabic numerals. Materials are organized from general to specific in all LC classification letters. For example, Language and Literature falls under the P classification. More specific subdivisions are achieved by adding an additional letter to the general classification. For example, American Literature falls under the PS call letters, while English or British Literature falls under the PR call letters. The system allows for further subdivisions by assigning numbers, so that books about Nineteenth Century American Literature fall into the PS500s and books by and about Nineteenth Century American Authors begin with the PS1000 call numbers. The arrangement includes individual classifications for authors. For example, books by and about William Faulkner fall into the PS3511.A86 call letters. An individual book by Faulkner would have additional letters and numbers appended to this call number. For example, Faulkner's novel A Light in August has the call number PS3511.A86L5. LC classification allows for very specific assignment of call numbers and, therefore, very precise arrangement of materials on the shelves.  

Although no one can be expected to memorize such an intricate system of classification, learning your own subject interest's classification scheme will allow you to go into a completely different library that uses LC classification and walk directly to the section of the stacks where your interests lie.  

Page updated 01/09