The Dewey Decimal Classification

The Dewey Decimal Classification (DDC) is virtually universal in the UK public library system, as well as being used in most academic libraries. In the United States it is challenged by the Library of Congress system (LC), but is still very widely used. It is therefore a good idea to know how it works and therefore how best to find one’s way round a library that is classified accordingly.

The principle devised by Melvil Dewey in 1876 was that all knowledge could be divided into ten parts, each of which could also be divided into ten, and so on. An infinite number of subdivisions of knowledge was therefore possible, and so any book in a library could be assigned a classification number that placed it within a subject category. Books on the same subject would be given the same number and so be placed together on the shelves.

Dewey’s original ten classes were as follows:

000 Generalities

100 Philosophy

200 Religion

300 Social Sciences

400 Language

500 Pure Science

600 Applied Science

700 The Arts

800 Literature

900 History

To take one of the above divisions and show its further subdivisions:

300 Social sciences (general)

310 Statistics

320 Politics

330 Economics

340 Law

350 Public Administration

360 Social Services

370 Education

380 Commerce

390 Customs and Etiquette

Each of these has a potential ten further subdivisions, after which a decimal point can be added and another digit placed after it, then as many digits as might be thought necessary to specify the subject in sufficient detail, each extra digit giving the possibility of a division into ten related categories.

One advantage of the Dewey system is that it indicates at the outset whether the document in question is general in nature or highly specific, simply from the length of the number on the label; the longer the string of numbers, the more detailed the contents. All Dewey numbers must contain a minimum of three digits, but if the third digit is a zero you know that it belongs to one of the first hundred divisions, and is therefore general in scope. Likewise, a book with just “700” on the spine would be a very generalised volume on the “The Arts” that could not be given a more specific classification.

There are clearly many disadvantages with the Dewey system, one obvious one being the highly artificial nature of the original division, and the assumption that knowledge can be conveniently sliced into divisions of ten, no more and no less. The problem of the original scheme is clear from the outset. Why, for example, should “Philosophy” be given the same status as “Pure Science”? Why should “Language” be placed so far from “Literature”?

There are plenty of other drawbacks, such as the problem of needing to update the scheme at fairly frequent intervals. There are also a number of other complications, such as the use of “auxiliary tables” to add such things as country subdivisions in a systematic way to a wide range of subjects.

However, from the point of view of the library user, the DDC soon becomes second nature, and finding items on shelves is a fairly straightforward process. The books (or videos, CDs or whatever) are shelved in a single numerical sequence from 000 to 999. In a large library, these may be split between a number of rooms or floors, or even separate libraries. For example, in a university library all the 340s might be housed in a special library devoted to law, possible housed next to the Law Department.

The library user can use a catalogue (these days it will usually be an online or computerised catalogue, whereas formerly it would have been a card catalogue) to look up the author and title of the item they want and note down the Dewey number. They can then go to the shelves and walk along until they find the number and the item they want.

For example, a book on 19^th century British poetry might have the number 821.809 (800 is Literature, 820 is Literature in English, 821 specifies poetry, 821.8 indicates the period, and 821.809 shows the country). The searcher must therefore find each digit in turn, narrowing the search to 800, then going past the 810s but not as far as the 830s, then making sure to limit the search to 821, and so on.

It is quite likely that a large library will have a lot of items with the same number, so the use of the first three letters of the author’s name is common on library labels. For example, the book “A history of English” by Barbara Fennell might have the label 420.9 FEN to make it easy to find among all the other books with the same Dewey number.

Many library users are not looking for a particular book but wish to browse along the shelves and choose something that takes the eye. The Dewey system makes this very easy. If they simply want, for example, to browse for something on “American history” they can just note the number “973” and go to that point on the shelves. They know that anything that starts with those three digits will be on American history, and so will anything that has more digits following on, such as 973.1, 973.2, etc for subdivisions by period of history.

Despite the many problems that the Dewey system presents to modern librarians, it works for most practical purposes. The contrast between the organization of a library and the disorganization of the World Wide Web, for example, is striking. The contrast can be seen most clearly, and to Dewey’s advantage, when a general item is being sought. Web search engines only work when the subject being sought is of a specific nature, such that the more keywords you enter the more likely you are to get something that fits the bill. With generalities they are far less satisfactory. Just try entering “Law” as a search term in Google and see where it gets you! Dewey wins hands down on these occasions!

© John Welford