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Understanding Call Numbers: The Dewey Decimal System

What is the Dewey Decimal System?

The Dewey Decimal Classification system is a classifying system used by libraries to organize their collections. It was first introduced to the public in 1876 by Melvil Dewey, a founding member of the American Library Association. It is the most widely used classification system in the world. Libraries in over 140 countries use the system to organize and provide access to their collections. At NICC, you'll find the library is organized using Dewey Decimal Classification. 


How does the Dewey Decimal system work?

The Dewey Decimal system is subject based. That's one of the great things about the system; you don't need the names of authors or book titles if you are looking for books on a certain topic. You just need the call number, which is the group of numbers you'll find on the spine of a book. Specific call numbers for a particular item will vary from library to library depending on how the library chooses to classify their collection, but generally Dewey Decimal libraries will follow the same system of assigning a call number to an item (or they'll just use the Dewey Decimal number assigned to the item by the Library of Congress).

Each item is assigned a three digit number, which corresponds to a broad subject group that the item would fall under. There are ten broad subject headings:

000s: Computer science, information, & general works

100s: Philosophy & psychology

200s: Religion

300s: Social sciences

400s: Language

500s: Science

600s: Technology

700s: Arts & recreation

800s: Literature

900s: History & geography

As you can imagine, these topics are incredibly broad. Take the 600s, for example--the subject is "Technology." This covers a whole slew of topics, everything from medicine to animal husbandry to metallurgy. If you want to research applied physics, you don't want to waste time looking through books on child rearing. So, how do you narrow down your search?

The Dewey Decimal system further breaks these subjects into subclasses by adding two digits. For example:

800: Literature

820: English and Old English literatures

823: English fiction

As the number becomes more specific, so does the subject matter. So if we are looking to browse English fiction, we found the right spot. Every book/item with the call number 823 will correspond to the subject of English fiction. Around 823 we'd find related subjects. 822 would be English drama and 824 indicates English essays.

But what if we are looking for something even more specific? Or even a particular title? After all, the English have written a lot of fiction and finding a certain book in a sea of many would be difficult, or at least time consuming. If the library has a need for even more specificity (which usually they do) the three digit number will be followed by a decimal point and even more numbers. This is where things can get complicated and even a little messy, because there is no rule for how many numbers are needed after the decimal point. The more numbers, the more specific the subject. No need to panic though. Libraries typically only add as many numbers as they need. The smaller the collection on a certain subject, the less specific they need to get with their organization. Here at NICC you'll typically find anywhere from one to five numbers after a decimal point. So let's pretend we want English fiction from the first half the 20th century and take a look at our example again:

823: English fiction

823.9: Modern Period

823.91: 1901-1999 (20th century)

823.912: 1901-1945

As you can see and as mentioned before, the more specific the number gets, the more specific a topic is. So now we have located all the English fiction from 1901-1945. If we decided we actually wanted, let's say, English fiction from 1945-1999, we wouldn't have to go far; the call number for the subject is 823.914. Related subjects will usually be close by.

But maybe we really wanted to read The Silmarillion by J R R Tolkien. How would we go about finding that? We are already so specific with our call number, and at this point even the Library of Congress says, that's enough with the numbers for this book. Now the library will transition to using what's known as a cutter. Here at NICC we use three letters for our cutters. First, if the work has an author, we will use the first three letters of the author's last name. If the work is an edited piece or does not have an author, we use the first three letters of the title. In the case of The Silmarillion our cutter is "Tol" for Tolkien. If there was no author or the book had an editor instead of an author, we would would use "Sil" for Silmarillion (we ignore non-significant words, like 'a,' 'an,' or 'the').

So for The Silmarillion by J R R Tolkien, we would head to the 800s section and look for the complete call number with the cutter of 823.912 Tol. And there we would find that very specific book we were looking so hard for.


Use the catalog and ask a librarian

Now you understand how the Dewey Decimal Classification system works. But this explanation isn't exactly completely helpful. You know now that similar subjects are going to be found around the same area, but that doesn't help you figure out the call number in the first place. After all, how are you to know that call number 487.1 corresponds to Mycenaean language? Well, you won't know (or at least we don't expect you to). This is where the library catalog and your local friendly librarian come in handy. Head to the online library catalog, search for the subject you are interested in, and browse until you find a book that pertains to your subject. Once you find something that looks promising, take a look at the call number and head to that section in the library to find that source and other items on the same subject.

Don't be afraid to ask the librarians either. They are there to help and we promise they don't bite. They are pretty good at finding materials that you might not have thought of (487.1 is Mycenaean language but you might find some relevant information in Mycenaean history under 939.18). Feel free to stop by the circulation desk, give us a call, or shoot us a message online. 

To the left you'll find some basic Dewey Decimal summaries to help you begin your search or just to browse. Also included are some overarching topics and the different call numbers under which you can find them.