Understanding ‘Class … in…’ Notes in Dewey Decimal Classification

When you open the schedules of the Dewey Decimal Classification (DDC) and look closely at any class number, you will often find small lines of instruction printed below the heading. These are notes, and they quietly do the heavy lifting of keeping the entire system consistent. One particularly useful type is the ‘Class … in…’ note. It tells you to take a specific topic and place it at a number that is different from where you might first expect. For a beginner in document processing, understanding this note is the difference between guessing a class number and assigning it with confidence.

What are ‘Class … in…’ notes? 🔗

A ‘Class … in…’ note is a direct instruction to the classifier. It follows a simple pattern: the word “Class,” followed by a specific topic, followed by the word “in,” and then the class number where that topic belongs. The structure looks like this: Class [a particular topic] in [a particular number].

These notes belong to a larger family known as class-elsewhere notes. The rule is easy to remember: almost every note that begins with the word “class” is a class-elsewhere note, with one exception, the “class here” note. So when you see a note starting with “Class charts…,” “Class works on…,” or “Class comprehensive works…,” you are reading an instruction to send that material somewhere other than the number you are currently looking at.

In short, a ‘Class … in…’ note carves out a narrow slice of a broad subject and redirects it to a more precise home. It prevents a specific aspect from being lumped together with everything else under a general heading.

Where these notes sit in the schedules 🔗

DDC notes are not placed randomly. They appear in a fixed order under a heading, moving from notes that describe what belongs at the number to notes that point away from it. The order of notes generally runs from definition and scope notes, through “including” and “class here” notes, and finally to class-elsewhere notes and references. Because the ‘Class … in…’ note is a redirecting instruction, it usually appears later in this sequence, after the notes that tell you what the number actually covers. Knowing this order helps you read an entry the way it was designed to be read.

The purpose of these notes 🔗

The main job of a ‘Class … in…’ note is to ensure the proper placement of subjects. DDC is built on a principle that surprises many students at first: it is arranged by discipline, not by subject. The same topic can appear in several different classes depending on how it is treated. Clothing, for example, is classed in one place when studied as psychology, another when studied as custom, and yet another when studied as fashion design.

This discipline-based approach creates a practical problem. A single book may contain material that, by its specific nature, belongs in a narrower or different number than the broad heading suggests. Without guidance, two catalogers could easily place the same item in two different numbers. The ‘Class … in…’ note removes that uncertainty. It acts as a fixed signpost, telling every classifier exactly where a particular type of material should go.

Distinguishing between general and specific treatment 🔗

A broad class number is meant to hold general or comprehensive works on a subject. But a subject often has specialised forms, charts, photographs, statistics, or particular applications, that deserve their own precise number. The ‘Class … in…’ note draws this line clearly. It separates the general treatment of a topic, which stays at the main number, from a specific treatment, which is sent elsewhere. This separation keeps each number meaningful and stops a general heading from quietly swelling with material that should have been scattered to more exact locations.

Examples in action 🔗

The clearest way to understand this note is through a worked example. Consider a heading dealing with the Moon in the astronomy class. Below it, you might find an instruction such as:

Class charts and photographs of the moon in 523.39

Here is what this is doing. General works about the Moon as a celestial body sit at the broader astronomy number for the Moon. But charts and photographs of the Moon are a specific kind of material. The note redirects them to 523.39, a more precise number meant for that purpose. A cataloger handling a lunar photographic atlas would read this note and immediately know not to place it with general works on the Moon, but to assign 523.39 instead.

The logic repeats across the schedules. A heading on a broad subject will carry a note pulling out one narrow aspect, statistics on a topic, a specific application of a technology, or works limited to one region, and direct it to the number built for that aspect. Each note is small, but together they form a network that keeps related materials precisely sorted.

How it differs from a ‘Class here’ note 🔗

It helps to contrast the two. A “class here” note pulls material toward the current number, telling you that certain topics, even ones broader or narrower than the heading, belong right here. A ‘Class … in…’ note does the opposite. It pushes a specific topic away to a different number. One gathers, the other redirects. Reading both correctly is essential, because mistaking a redirect for an inclusion is one of the most common errors a new classifier makes.

How they improve classification accuracy 🔗

The deeper value of these notes lies in how they protect the accuracy and consistency of the whole system. Their central contribution is that they prevent overlap between subjects.

Resolving the problem of multiple possible numbers 🔗

Because DDC scatters a subject across disciplines, a single item can often seem to fit two or three numbers at once. Class-elsewhere notes, including the ‘Class … in…’ form, exist precisely to settle these conflicts. They distinguish among numbers in the same hierarchy, lead the classifier toward interrelated topics, and point to broader or narrower numbers that might otherwise be overlooked. When a note tells you a specific aspect goes “in” a stated number, the competing options simply fall away. There is no longer a judgment call to make.

Keeping related materials together and unrelated materials apart 🔗

Accuracy in classification is not only about a single book. It is about how an entire collection behaves on the shelf. If charts and photographs of the Moon are consistently sent to one number while general lunar works stay at another, then a reader browsing either location finds a coherent, predictable set of materials. The notes ensure that what belongs together stays together, and what should be separated stays separated. This is what gives DDC its reliability across the more than one hundred and thirty countries that use it.

Scatter notes and broad direction 🔗

Some redirecting notes do not point to a single number. A scatter note leads to many locations at once, instructing the classifier to place a topic with whatever subject it happens to concern. While a basic ‘Class … in…’ note usually names one precise destination, recognising that the class-elsewhere family also includes these scatter instructions helps you handle entries where the redirection is spread across the schedules rather than fixed to one number.

Reading these notes with confidence 🔗

For students of document processing, the practical takeaway is straightforward. When you sit with a DDC schedule and a book in hand, do not stop at the heading. Read every note beneath it. A note that begins with “Class” and contains “in” followed by a number is not optional advice, it is a binding instruction. Treat it as the final word on where that specific material belongs.

An instruction note of this kind explains both the contents of a class and its relationship to other classes. Once you train your eye to spot the pattern, classification becomes far less about intuition and far more about following clear, documented direction. This is exactly the discipline that separates a careful cataloger from a hesitant one, and it is a habit worth building early. Over time, the notes stop feeling like obstacles and start working as the reliable guides they were always meant to be.

What do you think? If you came across a book of lunar photographs without any note to guide you, where would your instinct tell you to place it, and how might that differ from the number DDC actually intends? And do you think a discipline-based system that scatters one subject across many numbers ultimately serves readers better than a system that keeps every aspect of a subject in one place?

References

1. https://socialsci.libretexts.org/Courses/Sacramento_City_College/LIBT331:_Library_Cataloging_Procedures_(Li)/01:_Cataloging_Rules_and_Tools/1.04:_Classification_systems_-_Library_of_Congress/1.4.03:_Introduction_to_the_Dewey_Decimal_Classification
2. https://wikieducator.org/Dewey_Decimal_classification
3. https://en.wikipedia.org/wiki/List_of_Dewey_Decimal_classes
4. https://help.oclc.org/Librarian_Toolbox/OCLC_glossaries/Dewey_Decimal_Classification_glossary