This Is How We Dewey: A Primer

A Teach Me How To Dewey production


Ready for the Snapchat summary of Dewey? Here it goes:

The Dewey Decimal Classification (DDC) organizes library material in a numerical hierarchy by field of study. Each one has its own 100-level placement, called a class:

  • 000 – General works, Computer science and Information
  • 100 – Philosophy and psychology
  • 200 – Religion
  • 300 – Social sciences
  • 400 – Language
  • 500 – Science
  • 600 – Technology
  • 700 – Arts & recreation
  • 800 – Literature
  • 900 – History & geography

Each class has its own 10 subdivisions, which have their own subsections, which become more specific the deeper they go. So a book with a Dewey number of 300 will be more general than one with 301.355. Books are organized on the shelf in numerical order, with books with the same Dewey number organized alphabetically by author. (It’s a lot easier to understand when you see it on the shelves, so go visit your local library!)

A book’s Dewey number has two components: its class number (i.e. a number that designates its place on the shelves) and three letters, which usually are the first three of the author’s last name.

So in my library, David McCullough’s Truman has a Dewey number of 973.918 MCC, which got that because it’s in:

900 History & geography
– 970 General history of North America
– – 973 General history of North America; United States

The numbers after the decimal point identify the material more and more specifically by geography, subject, language, etc. And because David McCullough was the author, MCC is tagged onto the end.

That’s basically it. How an item gets cataloged fully – with subject headings, physical description, and all that extra info most non-library folks don’t care about – is both an art and a science, and one best left to professional catalogers because they actually enjoy doing it. But going forward, we’ll be just fine with the basic knowledge of what a Dewey number is and why it’s important for libraries.

Two-minute tutorial done. Let’s Dewey this!


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