Library classification systems

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Up to the 19th century, many libraries simply arranged their books by size and date of acquisition. Individual books could be found through a catalogue. Others used simple classifications. Increasing public access and size led to the introduction of various more sophisticated library classification systems, of which some important or distinctive ones are briefly covered below.

Decimal classification (1st edition, Melvil Dewey, 1876; 23rd edition, 4 volumes, Online Computer Library Center, 2011)

This system is distinctive in its use of numerals for top-level classes, as most use letters. These are as follows:

  • 100 Philosophy and psychology
  • 200 Religion
  • 300 Social sciences
  • 400 Language
  • 500 Pure science
  • 600 Technology
  • 700 Arts and recreation
  • 800 Literature
  • 900 History and geography

Further subdivisions are made by adding digits in place of zeros: 510 mathematics, 423 English dictionaries etc. Beyond this, decimal points are used: 794.1 chess etc. Books of a more general nature are not so subdivided, but have their own subdivisions: 033 German encyclopaedias, 501 philosophy of science etc.

There is no specification for the order of books within the lowest levels of classification (originally it was to be by order of acquisition). Libraries generally arrange books alphabetically by author, or just at random. Order of books by the same author is variously by title, date or size in different libraries.

This system is used in most libraries in the English-speaking world. Note, however, that it is used, not followed. In particular, it is usually ignored for fiction, which it would distribute among various national literatures: 813 American fiction, 823 British fiction etc. Most libraries put all fiction in English (including translations from other languages) in alphabetical sequence outside the classification.

There is a "fork" of this system called the Universal Decimal Classification, originated in Belgium. It drops trailing zeros and incorporates language with literature, so that 8 covers literature and language.

Expansive classification (Charles Ammi Cutter, 1891-1903)

Cutter was responding to complaints by custodians of small libraries that systems such as the decimal classification were too complicated for their purposes. The expansive classification is in fact a series of seven classifications for libraries of different sizes, the last of which was not quite finished by the time of Cutter's death. Libraries with some degree of specialization might use different levels in different fields. The lowest level has just eight classes. Cutter gives two versions of this in his book of the first six levels, in the introduction and main body. Possibly he revised one but forgot to revise the other. These are as follows:

  • A Reference and general (Cutter regards Reference as a "form" class like literature, generally characterized by alphabetical arrangement)
  • B Philosophy and religion
  • E Historical sciences, or subdivided:
    • E Biography
    • F History and geography and travels
  • H Social sciences
  • L Natural sciences and arts
  • Y Language and literature, or subdivided:
    • X Language
    • Y Literature
  • YF Fiction

As the system is expanded, more letters are brought in and subdivisions added. The subdivisions are mainly by further letters, with numerals reserved for standard tables such as geographical areas.

Within the lowest classes arrangement is recommended to be alphabetically by author and title.

This system is used in a few libraries in New England, but its top-level classes were also used as the basis for those in the Library of Congress.

Library of congress classification (Herbert Putnam, 1897)

This system uses two letters, or occasionally three, followed by numerals. Thereafter the Library arranges by author and date.

It is used in many academic libraries, particularly in the USA.

Subject classification (James Duff Brown, 1906)

In most systems books are arranged by "discipline", i.e. the approach adopted to the subject matter (more precisely, the approach of the reader, not the author, so history and philosophy of science go under science because they are mainly of interest to those interested in science). This system arranges by subject instead, so that all books about coffee go together, under E917, rather than being distributed among agriculture, cookery etc.

This system is used in Islington library.

Colon classification (1st edition, S. R. Ranganathan, 1933; 6th edition, 1960; 7th edition, volume 1, posthumously completed by M. A. Gopinath, 1987)

This is the first attempt at what Ranganathan named "faceted" classification. As he acknowledged, some of this already existed. For example, in the decimal classification, history of the USA is 973, geography of the USA is 917.3, art of the USA is 709.73 etc. Ranganathan systematically applied a method of classification throughout, involving five facets, called personality, matter, energy, space and time. The first three of these are applied more or less metaphorically depending on the field. They were originally delimited by colons, whence the name, but later each was given its own punctuation mark.

This system corrects Western bias found in other systems. For example, in the decimal classification, most subdivisions of 200 religion are to do with Christianity, and most of 400 language and 800 literature are allocated to European languages and their literatures. (But history and geography do not have this bias.)

Within the lowest levels of classification, the preferred arrangement is chronological, not alphabetical.

This system is used in many Indian libraries.

Bibliographic classification (1st edition, Henry Evelyn Bliss, 4 volumes, 1940-53; 2nd edition, Bliss Classification Association, 1977- , in progress)

This system takes the idea of faceted classification further, with as many as thirteen facets.

Although originally American, it has become more successful in Britain; in particular, a number of Oxbridge colleges use it.

BISAC (Book Industry Standards And Communications)

This has 53 top-level classes indicated by three-letter codes, from ANT antiques and collectibles to YAN young adult[1] non-fiction. Subdivisions are indicated by numerals, but they too are arranged alphabetically.

This system has been in use by bookshops for a long time, but has only comparatively recently been adopted by some libraries.


  1. A euphemism for teenagers.