Dewey Decimal Classification

The Dewey Decimal Classification system is a method for classifying books and materials inside libraries designed by Melvil Dewey, an American librarian. It uses a floating decimal number to represent the subject of a book. There are 999 top-level categories - the highest-level of the taxonomy is represented by the first digit, then the second and third digits. After that, the numbers after the decimal point specify the subject as far as it needs to go.

For instance, the 100 range covers philosophy, psychology and paranormalism. Within there, metaphysics is to be found at 110, ontology at 111 and paranormal phenomena is at 130. The Dewey system is widely used, but many find faults with it. Dewey artificially slices complex matters in order to fit everything into a decimal organisation. This can be reflected rather strangely on the shelf. The 100s are a perfect example, with academic philosophy books being mixed together with books on astrology and graphology. Similarly, in the 200 range, where religion is covered, Dewey is heavily oriented towards Christianity - as can be expected from someone in 19th century America - but it does cause categorisation to become interesting: Christianity and general religious topics are mixed together for categories 200-289, leaving 290 for "Other and comparative religions" - Judaism gets 296, while "Religions of Indic origin" gets 294. The whole system can often feel unbalanced.

While the Dewey system is widely used in many libraries at the local and school level, some academic, research and national libraries use different systems. The Library of Congress uses its own system, as does the British Library in London. The libraries of the University of Oxford, University of London, University of Chicago, Duke University and many others are also using other systems, some based on the Library of Congress, others home-grown.