Introduction

to the
Dewey Decimal Classification
About the Introduction
1.1 This Introduction explains the basic principles and structure of the Dewey Deci-
mal Classification (DDC) system.
1.2 The Introduction is intended to be used in conjunction with the Glossary and
the Manual. The Glossary defines terms used in the Introduction and elsewhere
in the Classification. The Manual offers advice on classifying in difficult areas,
and explains how to choose between related numbers.

Classification: What It Is and What It Does

2.1 Classification provides a system for organizing knowledge. Classification may
be used to organize knowledge represented in any form, e.g., books, documents,
electronic resources.
2.2 Notation is the system of symbols used to represent the classes in a classifica-
tion system. In the Dewey Decimal Classification, the notation is expressed in
Arabic numerals. The notation gives both the unique meaning of the class and
its relation to other classes. The notation provides a universal language to iden-
tify the class and related classes, regardless of the fact that different words or
languages may be used to describe the class.

History, Current Use, and Development of the Dewey Decimal

Classification
3.1 The Dewey Decimal Classification—conceived by Melvil Dewey in 1873 and
first published in 1876—is a general knowledge organization tool that is con-
tinuously revised to keep pace with knowledge. The system is further extended
through number building, interoperable translations, association with catego-
rized content, and mappings to other subject schemes.
3.2 The DDC is published in full and abridged editions by OCLC Online Computer
Library Center, Inc. The abridged edition is a logical truncation of the notational
and structural hierarchy of the corresponding full edition on which it is based,
and is intended for general collections of 20,000 titles or less. Both editions are
issued in print and electronic versions; the electronic versions are updated fre-
quently and contain additional index entries and mapped vocabulary. OCLC
owns all copyright rights in the Dewey Decimal Classification, and licenses the
system for a variety of uses.
3.3 The DDC is the most widely used classification system in the world. Librar-
ies in more than 138 countries use the DDC to organize and provide access to
their collections, and DDC numbers are featured in the national bibliographies

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 Dewey Decimal Classification

of more than sixty countries. Libraries of every type apply Dewey numbers on
a daily basis and share these numbers through a variety of means (including
WorldCat). Dewey is also used in a variety of applications on the web in support
of categorization, browsing, and retrieval.
3.4 The DDC has been translated into over thirty languages. Since 1988, authorized
translations of the full and abridged editions of the DDC have been published or
are under way in Arabic, French, German, Greek, Hebrew, Icelandic, Indone-
sian, Italian, Norwegian, Russian, Spanish, Swedish, Turkish, and Vietnamese.
The DDC Summaries, the top three levels of the Dewey Decimal Classification
system, have been translated into Afrikaans, Arabic, Chinese, Czech, French,
German, Hebrew, Italian, Norwegian, Portuguese, Russian, Scots Gaelic, Span-
ish, Swedish, and Vietnamese.
3.5 One of Dewey’s great strengths is that the system is developed and maintained
in a national bibliographic agency, the Library of Congress. The Dewey edito-
rial office is located in the Dewey Section of the Library of Congress, where
classification specialists annually assign over 60,000 DDC numbers to records
for works cataloged by the Library. Having the editorial office within the Dewey
Section enables the editors to detect trends in the literature that must be incor-
porated into the Classification. The editors prepare proposed schedule revisions
and expansions, and forward the proposals to the Decimal Classification Edito-
rial Policy Committee (EPC) for review and recommended action.
3.6 EPC is a ten-member international board whose main function is to advise the
editors and OCLC on matters relating to changes, innovations, and the general
development of the Classification. EPC represents the interests of DDC users;
its members come from national, public, school, and academic libraries, and
from library schools.

Overview of the Dewey Decimal Classification

Conceptual F ramework
4.1 The DDC is built on sound principles that make it ideal as a general knowl-
edge organization tool: meaningful notation in universally recognized Arabic
numerals, well-defined categories, well-developed hierarchies, and a rich net-
work of relationships among topics. In the DDC, basic classes are organized by
disciplines or fields of study. At the broadest level, the DDC is divided into ten
main classes, which together cover the entire world of knowledge. Each main
class is further divided into ten divisions, and each division into ten sections
(not all the numbers for the divisions and sections have been used).
4.2 The main structure of the DDC is presented in the DDC Summaries preced-
ing the schedules. The first summary contains the ten main classes. The second
summary contains the hundred divisions. The third summary contains the thou-
sand sections. The headings associated with the numbers in the summaries have
been edited for browsing purposes, and do not necessarily match the complete
headings found in the schedules.

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 Introduction

4.3 The ten main classes are:

000 Computer science, information & general works
100 Philosophy & ­psychology
200 Religion
300 Social sciences
400 Language
500 Science
600 Technology
700 Arts & recreation
800 Literature
900 History & geography
4.4 Class 000 is the most general class, and is used for works not limited to any one
specific discipline, e.g., encyclopedias, newspapers, general periodicals. This
class is also used for certain specialized disciplines that deal with knowledge
and information, e.g., computer science, library and information science, jour-
nalism. Each of the other main classes (100–900) comprises a major discipline
or group of related disciplines.
4.5 Class 100 covers philosophy, parapsychology and occultism, and psychology.
4.6 Class 200 is devoted to religion.
4.7 Class 300 covers the social sciences. Class 300 includes sociology, anthropol-
ogy, statistics, political science, economics, law, public administration, social
problems and services, education, commerce, communications, transportation,
and customs.
4.8 Class 400 comprises language, linguistics, and specific languages. Literature,
which is arranged by language, is found in 800.
4.9 Class 500 is devoted to the natural sciences and mathematics.
4.10 Class 600 is technology.
4.11 Class 700 covers the arts: art in general, fine and decorative arts, music, and the
performing arts. Recreation, including sports and games, is also classed in 700.
4.12 Class 800 covers literature, and includes rhetoric, prose, poetry, drama, etc.
Folk literature is classed with customs in 300.
4.13 Class 900 is devoted primarily to history and geography. A history of a specific
subject is classed with the subject.
4.14 Since the parts of the DDC are arranged by discipline, not subject, a subject
may appear in more than one class. For example, “clothing” has aspects that fall
under several disciplines. The psychological influence of clothing belongs in
155.9 as part of the discipline of psychology; customs associated with clothing
belong in 391 as part of the discipline of customs; clothing in the sense of fash-
ion design belongs in 746.9 as part of the discipline of the arts.

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 Dewey Decimal Classification

Notation
4.15 Arabic numerals are used to represent each class in the DDC. The first digit in
each three-digit number represents the main class. For example, 500 represents
science. The second digit in each three-digit number indicates the division. For
example, 500 is used for general works on the sciences, 510 for mathematics,
520 for astronomy, 530 for physics. The third digit in each three‑digit number
indicates the section. Thus, 530 is used for general works on physics, 531 for
classical mechanics, 532 for fluid mechanics, 533 for gas mechanics. The DDC
uses the convention that no number should have fewer than three digits; zeros
are used to fill out numbers.
4.16 A decimal point, or dot, follows the third digit in a class number, after which
division by ten continues to the specific degree of classification needed. The dot
is not a decimal point in the mathematical sense, but a psychological pause to
break the monotony of numerical digits and to ease the transcription and copy-
ing of the class number. A number should never end in a 0 anywhere to the right
of the decimal point.

P rinciple of H ierarchy
4.17 Hierarchy in the DDC is expressed through structure and notation.
4.18 Structural hierarchy means that all topics (aside from the ten main classes) are
part of all the broader topics above them. The corollary is also true: whatever
is true of the whole is true of the parts. This important concept is called hierar-
chical force. Certain notes regarding the nature of a class hold true for all the
subordinate classes, including logically subordinate topics classed at coordi-
nate numbers. (For a discussion of notes with hierarchical force, see paragraphs
7.10–7.16 and 7.18–7.20.)
Because of the principle of hierarchical force, hierarchical notes are usually
given only once—at the highest level of application. For example, the scope
note at 700 applies to 730, to 737, and to 737.4. The words “Description, critical
appraisal . . .” found in the scope note at 700 also govern the critical appraisal of
coins in 737.4 Coins. In order to understand the structural hierarchy, the classi-
fier must read up and down the schedules (and remember to turn the page).
4.19 Notational hierarchy is expressed by length of notation. Numbers at any given
level are usually subordinate to a class whose notation is one digit shorter; coor-
dinate with a class whose notation has the same number of significant digits;
and superordinate to a class with numbers one or more digits longer. The under-
lined digits in the following example demonstrate this notational hierarchy:

600 Technology (Applied sciences)
630 Agriculture and related technologies
636 Animal husbandry
636.7 Dogs
636.8 Cats

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 Introduction

“Dogs” and “Cats” are more specific than (i.e., are subordinate to) “Animal hus-
bandry”; they are equally specific as (i.e., are coordinate with) each other; and
“Animal husbandry” is less specific than (i.e., is superordinate to) “Dogs” and
“Cats.”
4.20 Sometimes, other devices must be used to express hierarchy when it is not possi-
ble or desirable to do so through the notation. A see reference leads the classifier
to subdivisions of a subject located outside the notational hierarchy. A centered
entry (so called because its numbers, heading, and notes appear in the center of
the page) constitutes a major departure from notational hierarchy. A centered
entry is used to indicate and relate structurally a span of numbers that together
form a single concept for which there is no specific hierarchical notation avail-
able. In the DDC, centered entries are always flagged typographically by the
symbol > in the number column.

Classifying with the DDC

5.1 Classifying a work with the DDC requires determining the subject, the dis-
ciplinary focus, and, if applicable, the approach or form. (For a discussion of
approach or form, see paragraph 8.3.)

Determining the Subject of a Work

5.2 Classifying a work properly depends first upon determining the subject of the
work in hand. A key element in determining the subject is the author’s intent.
(A) The title is often a clue to the subject, but should never be the sole source
of analysis. For example, Opera could be the title of a work on the famil-
iar dramatic musical art form or on the web browser Opera. Likewise,
a title with specific terms that are subdivisions of a field may in fact
use such terms symbolically to represent the broader topic. For exam-
ple, titles containing terms like chromosomes, DNA, double helix, genes,
and genomes may use these terms symbolically to represent the whole
subject of biochemical genetics.
(B) The table of contents may list the main topics discussed. Chapter head-
ings may substitute for the absence of a ­table of contents. Chapter sub-
headings often prove useful.
(C) The preface or introduction usually states the author‘s purpose. If a fore-
word is provided, it often indicates the subject of the work and suggests
the place of the work in the development of thought on the subject. The
book jacket or accompanying material may include a summary of the
subject content.
(D) A scan of the text itself may provide further guidance or confirm prelimi-
nary subject analysis.
(E) Bibliographical references and index entries are sources of subject infor-
mation.

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 Dewey Decimal Classification

(F) Cataloging copy from centralized cataloging services is often helpful by

providing subject headings, classification numbers, and notes. Such copy
appears in online services, and on the verso of the title page of many
books as part of Cataloging‑in‑Publication (CIP) data. Data from these
sources should be verified with the book in hand, since the cataloging
record is based on prepublication information.
(G) Occasionally, consultation of outside sources such as reviews, reference
works, and subject experts may be required to determine the subject of
the work.
Determining the Discipline of a Work
5.3 After determining the subject, the classifier must then select the proper disci-
pline, or field of study, of the work.
5.4 The guiding principle of the DDC is that a work is classed in the discipline for
which it is intended, rather than the discipline from which the work derives.
This enables works that are used together to be found together. For example, a
general work by a zoologist on agricultural pest control should be classed in
agriculture, not zoology, along with other works on agricultural pest control.
5.5 Once the subject has been determined, and information on the discipline has
been found, the classifier will turn to the schedules. The summaries are a good
means of mental navigation. The headings and notes in the schedules them-
selves and the Manual provide much guidance. The Relative Index may help by
suggesting the disciplines in which a subject is normally treated. (For a discus-
sion of the summaries, see paragraph 7.1; for a discussion of the Manual, see
paragraphs 10.1–10.6; for a discussion of the Relative Index, see paragraphs
11.1–11.15.)
5.6 If the Relative Index is used, the classifier must still rely on the structure of the
Classification and various aids throughout to arrive at the proper place to clas-
sify a work. Even the most promising Relative Index citations must be verified
in the schedules; the schedules are the only place where all the information
about coverage and use of the numbers may be found.

More Than One Subject in the Same Discipline

5.7 A work may include multiple subjects treated separately or in relation to one
another from the viewpoint of a single discipline. Use the following guidelines
in determining the best placement for the work:
(A) Class a work dealing with interrelated subjects with the subject that is
being acted upon. This is called the rule of application, and takes pre-
cedence over any other rule. For instance, class an analytical work deal-
ing with Shakespeare’s influence on Keats with Keats. Similarly, class a
work on the influence of the Great Depression on 20th century American
art with American art.
(B) Class a work on two subjects with the subject receiving fuller treatment.

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 Introduction

(C) If two subjects receive equal treatment, and are not used to introduce
or explain one another, class the work with the subject whose number
comes first in the DDC schedules. This is called the first‑of‑two rule. For
example, a history dealing equally with the United States and Japan, in
which the United States is discussed first and is given first in the title, is
classed with the history of Japan because 952 Japan precedes 973 United
States.
Sometimes, specific instructions are given to use numbers that do not
come first in the schedules. For example, at 598, the note “class compre-
hensive works on warm-blooded vertebrates in 599” tells the classifier to
ignore the first-of-two rule and class a work on birds (598) and mammals
(599) in 599, which is the comprehensive number for warm‑blooded ver-
tebrates.
Also disregard the first‑of‑two rule when the two topics are the two
major subdivisions of a subject. For example, primary forms of energy
(333.792) and secondary forms of energy (333.793) taken together con-
stitute most of 333.79 Energy. Works covering both of these topics are
classed in 333.79 (not 333.792).
(For a discussion of comprehensive numbers, see paragraphs 7.16 and
7.18–7.19.)
(D) Class a work on three or more subjects that are all subdivisions of a
broader subject in the first higher number that includes them all (unless
one subject is treated more fully than the others). This is called the rule
of three. For example, a history of Portugal (946.9), Sweden (948.5), and
Greece (949.5) is classed with the history of Europe (940).
(E) Subdivisions beginning with zero should be avoided if there is a choice
between 0 and 1–9 at the same point in the hierarchy of the notation.
Similarly, subdivisions beginning with 00 should be avoided when there
is a choice between 00 and 0. This is called the rule of zero.
More Than One Discipline
5.8 Treating a subject from the point of view of more than one discipline is different
from treating several subjects in one discipline. Use the following guidelines in
determining the best placement for the work:
(A) Use the interdisciplinary number provided in the schedules or Relative
Index if one is given. An important consideration in using such an inter-
disciplinary number is that the work must contain significant material
on the discipline in which the interdisciplinary number is found. For
example, 305.231 (a sociology number) is provided for interdisciplinary
works on child development. However, if a work that is interdisciplinary
with respect to child development gives little emphasis to social devel-
opment and a great deal of emphasis to the psychological and physical
development of the child (155.4 and 612.6, respectively), class it in 155.4
(the first number in the schedules of the next two obvious choices). In

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 Dewey Decimal Classification

short, interdisciplinary numbers are not absolute; they are to be used

only when applicable. (For a discussion of interdisciplinary numbers, see
paragraphs 7.16, 7.18–7.19, and 11.8–11.9.)
(B) Class works not given an interdisciplinary number in the discipline
given the fullest treatment in the work. For example, a work dealing with
both the scientific and the engineering principles of electrodynamics
is classed in 537.6 if the engineering aspects are introduced primarily
for illustrative purposes, but in 621.31 if the basic scientific theories are
only preliminary to the author’s exposition of engineering principles and
practices.
(C) When classifying interdisciplinary works, do not overlook the possibili-
ties of main class 000 Computer science, information & general works,
e.g., 080 for a collection of interviews of famous people from various
disciplines.
Any other situation is treated in the same fashion as those found in the instruc-
tions at More Than One Subject in the Same Discipline (paragraph 5.7).

Table of Last R esort

5.9 When several numbers have been found for the work in hand, and each seems as
good as the next, the following table of last resort (in order of preference) may
be used as a guideline in the absence of any other rule:
Table of last resort
(1) Kinds of things
(2) Parts of things
(3) Materials from which things, kinds, or parts are made
(4) Properties of things, kinds, parts, or materials
(5) Processes within things, kinds, parts, or materials
(6) Operations upon things, kinds, parts, or materials
(7) Instrumentalities for performing such operations
5.10 Do not apply this table or any other guideline if it appears to disregard the
author’s intention and emphasis.

How Abridged Edition 15 Is Arranged

6.1 Abridged Edition 15 is composed of ten major parts:
(A) New Features in Abridged Edition 15: A brief explanation of the special
features and changes in Abridged Edition 15
(B) Introduction: A description of the DDC and how to use it
(C) Glossary: Short definitions of terms used in the DDC
(D) Index to the Introduction and Glossary
(E) Manual: A guide to the use of the DDC that is made up primarily of
extended discussions of problem areas in the application of the DDC.

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 Introduction

Information in the Manual is arranged by the numbers in the tables and

schedules
(F) Lists that compare Abridged Editions 14 and 15: Relocations and Discon-
tinuations, and Reused Numbers
(G) Tables: Four numbered tables of notation that can be added to class num-
bers to provide greater specificity
(H) DDC Summaries: The top three levels of the DDC
(I) Schedules: The organization of knowledge from 000–999
(J) Relative Index: An alphabetical list of subjects with the disciplines in
which they are treated subarranged alphabetically under each entry
Key Features of the Schedules and Tables
Summaries
7.1 Summaries provide an overview of the structure of classes. Two types of sum-
maries appear in the DDC:
(A) DDC Summaries, the summaries of the top three levels of the DDC, are
found in front of the schedules in volume 2. (For a discussion of DDC
Summaries, see paragraphs 4.2–4.13.)
(B) Single‑level summaries in the schedules and tables provide an overview
of classes with subdivisions that cover more than three pages. For exam-
ple, 380 Commerce, communications, transportation has the following
summary:

SUMMARY
381 Commerce (Trade)
382 International commerce (Foreign trade)
383 Postal communication
384 Communications
385 Railroad transportation
386 Inland waterway and ferry transportation
387 Water, air, space transportation
388 Transportation
389 Metrology and standardization
Entries
7.2 Entries in the schedules and tables are composed of a DDC number in the num-
ber column (the column at the left margin), a heading describing the class that
the number represents, and often one or more notes. DDC numbers are listed
in groups of three digits for ease of reading and copying. All entries (numbers,
headings, and notes) should be read in the context of the hierarchy. (For a dis-
cussion of the principle of hierarchy, see paragraphs 4.17–4.20.)
7.3 The first three digits of schedule numbers (main classes, divisions, sections)
appear only once in the number column, when first used. They are repeated at

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 Dewey Decimal Classification

the top of each page where their subdivisions continue. Subordinate numbers
appear in the number column, beginning with a decimal point, with the initial
three digits understood.
7.4 Table numbers are given in full in the number column of the tables, and are
never used alone. There are four numbered tables in Abridged Edition 15:
T1 Standard Subdivisions
T2 Geographic Areas, and Biography
T3 Subdivisions for Individual Literatures, for Specific Literary Forms
T4 Subdivisions of Individual Languages and Language Families
Except for notation from Table 1 (which may be added to any number unless
there is an instruction in the schedules or tables to the contrary), table notation
may be added only as instructed in the schedules and tables. (For a detailed dis-
cussion of the use of the four tables, see paragraphs 8.3–8.16.)
7.5 Some numbers in the schedules and tables are enclosed in parentheses or square
brackets. Numbers and notes in parentheses provide options to standard prac-
tice. Numbers in square brackets represent topics that have been relocated or
discontinued, or are unassigned. Square brackets are also used for standard sub-
division concepts that are represented in another location. Bracketed numbers
should never be used. (For a discussion of options, see paragraphs 12.1–12.7; for
a discussion of relocations and discontinuations, see paragraphs 7.22–7.23; for a
discussion of bracketed standard subdivisions, see paragraph 7.24.)
7.6 Standard subdivisions are also bracketed under a hook number, that is, a num-
ber that has no meaning in itself, but is used to introduce specific examples of a
topic. Hook numbers have headings that begin with “Miscellaneous,” “Other,”
or “Specific”; and do not contain add notes, including notes, or class-here notes.
For example:
  573.9 Miscellaneous systems and organs in animals,
regional histology and physiology in animals
  [.901–.909] Standard subdivisions
Do not use; class in 571.101–571.109
Notes
7.7 Notes are important because they supply information that is not obvious in the
notational hierarchy or in the heading with regard to order, structure, subordina-
tion, and other matters. Notes may appear in the record for a number or a span of
numbers. Notes may also appear at the beginning of a table. Footnotes are used
for instructions that apply to multiple subdivisions of a class, or to a topic within
a class. Individual entries in the Manual are also considered notes.
7.8 Notes in the schedules and tables generally appear in the following order: revi-
sion, former-heading, definition, number-built, standard-subdivisions-are
added, variant-name, scope, including, class-here, arrange, add (including sub-

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 Introduction

divisions-are-added), preference, class-elsewhere, see-reference, see-also refer-

ence, see-Manual, option, discontinued, and relocation notes.
7.9 The notes below do the following: (A) describe what is found in the class and
its subdivisions; (B) identify topics in standing room, i.e., topics with insuffi-
cient literature to have their own number; (C) describe what is found in other
classes; and (D) explain changes in the schedules and tables. Other notes are
described in the sections on number building (paragraphs 8.1–8.20), citation
and preference order (paragraphs 9.1–9.5), the Manual (paragraphs 10.1–10.6),
and options (paragraphs 12.1–12.5).
Notes in categories (A) and (C) have hierarchical force (i.e., are applicable to
all the subdivisions of a particular number). Those in category (B) do not have
hierarchical force.
(A) Notes That Describe What Is Found in a Class
7.10 Definition notes indicate the meaning of a term in the heading. For example:
364 Criminology
Crime and its alleviation
7.11 Scope notes indicate whether the meaning of the number is narrower or broader
than is apparent from the heading. For example:
700 The arts
Description, critical appraisal, techniques, procedures, apparatus,
equipment, materials of the fine, decorative, literary, performing,
recreational arts
7.12 Number-built notes identify and explain the source of built numbers included in
the schedules and tables. Built numbers are occasionally included in the sched-
ules or tables to provide additional information or to indicate exceptions to reg-
ular add instructions. For example:
822 English drama
Number built according to instructions under 821–828 and at
beginning of Table 3
7.13 Former-heading notes are given only when the heading associated with a class
number in the previous edition has been altered to such a degree that the new
heading bears little or no resemblance to the previous heading, even though the
meaning of the number has remained substantially the same. For example:
004.16 *Personal computers
Former heading: Microcomputers
7.14 Variant-name notes are used for synonyms or near synonyms. For example:

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 Dewey Decimal Classification

001.942 Unidentified flying objects (UFOs)

Variant name: flying saucers
7.15 Class‑here notes list major topics in a class. These topics may be broader or
narrower than the heading, overlap it, or define another way of looking at essen-
tially the same material. Topics in class-here notes are considered to approxi-
mate the whole of the class. For example:
371.04 Alternative schools
Class here experimental schools, free schools
Standard subdivisions may be added for any topic in a class-here note. (For a
detailed discussion of the use of standard subdivisions for concepts that approxi-
mate the whole of a class, see paragraphs 8.3–8.11 and the beginning of Table 1.)
7.16 Class‑here notes are also used to indicate where interdisciplinary and compre-
hensive works are classed. Interdisciplinary works treat a subject from the per-
spective of more than one discipline. For example:
391 Costume and personal appearance
Class here interdisciplinary works on costume, clothing (apparel,
garments), fashion; casual wear (sportswear)
Comprehensive works treat a subject from various points of view within a single
discipline. Comprehensive works may be stated or implied in a class-here note.
For example:
612 Human physiology
Class here comprehensive works on human anatomy and
physiology (stated)
—76 South central United States
Class here Gulf Coast states, Old Southwest (implied)
(B) Including Notes (Notes That Identify Topics in Standing Room)
7.17 Including notes identify topics that have “standing room” in the number where
the note is found. Standing room numbers provide a location for topics with
relatively few works written about them, but whose literature may grow in the
future, at which time they may be assigned their own number. For example:
362.16 Extended care medical facilities
Including convalescent homes, sanatoriums for people
suffering from chronic diseases
Including notes may also contain topics from subclasses in the full edition that
are not part in the notational framework of the abridged edition. For example:

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 Introduction

534 Sound and related vibrations

Including generation of sound, transmission of sound,
characteristics of sound
The topics in the including note under 534 in the abridged edition are drawn
from subclasses of 534 found only in the full edition: 534.1 Generation of sound,
534.2 Transmission of sound, and 534.3 Characteristics of sound.
Standard subdivisions cannot be added for topics in standing room, nor are
other number‑building techniques allowed.
(C) Notes That Describe What Is Found in Other Classes
7.18 Class‑elsewhere notes lead the classifier to interrelated topics, or distinguish
among numbers in the same notational hierarchy. They are used to show prefer-
ence order, to lead to the comprehensive or interdisciplinary number, to over-
ride the first-of-two rule, or to lead to broader or narrower topics in the same
hierarchical array that might otherwise be overlooked. They may point to a spe-
cific number, or to a concept scattered throughout the schedules. All notes that
begin with the word “class” are class‑elsewhere notes, except when they begin
with “class here.” For example:
641.7 Specific cooking processes and techniques
Class specific processes applied to specific materials in
641.6; class specific processes applied to specific kinds of
dishes, preparing beverages in 641.8
370.15 Educational psychology
Class behavior modification methods of instruction in
371.39; class interdisciplinary works on psychology in 150.
Class psychology of a specific topic in education with the
topic, plus notation 01 from Table 1, e.g., psychology of
special education 371.901
155.4 Child psychology
Class national psychology of children in
155.4093–155.4099; class general topics applied to
children by specific attributes in 155.42–155.45; class
socialization in 303.3; class interdisciplinary works on
child development in 305.231
7.19 See references lead from a stated or implied comprehensive number for a con-
cept to the component (subordinate) parts of that concept in a different notational
hierarchy. See references also lead from the interdisciplinary number for a con-
cept to treatment of the concept in other disciplines. A see reference may point
to a specific number, or to a concept scattered throughout the schedules. Each
see reference begins with the word “For” and appears in italics. For example:

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 Dewey Decimal Classification

577.7 Marine ecology

Class here saltwater ecology
For salt lake ecology, freshwater lagoons, see 577.63;
for saltwater wetland and seashore ecology, see 577.69
305.4 Women
Class here interdisciplinary works on women, on females
For a specific aspect of women not provided for here,
see the aspect, e.g., women’s suffrage 324.6, legal status
of women 346.01
Throughout Table 2, see references (often in footnote form) lead from the
implied comprehensive number for a jurisdiction, region, or feature to its subor-
dinate parts in other classes. For example:
—417 Republic of Ireland (Eire)
Class here *Shannon River
*For a specific part of this jurisdiction, region, or feature, see the part and
follow instructions under —4–9
7.20 See‑also references lead the classifier to related topics. They are reminders that
minor differences in wording and context can imply differences in classification.
Each see-also reference appears in italics. For example:
599.65 Deer
Including chital, muntjacs; Odocoileus; white-tailed
(Virginia) deer; mule deer; Cervus; fallow deer; elk
(moose); caribou (reindeer); roe deer
See also 599.63 for mouse deer
(D) Notes That Explain Changes or Irregularities in the Schedules and Tables
7.21 Revision notes warn users that there have been changes in the subdivisions of
a class since the previous edition. A new schedule, complete revision, or exten-
sive revision is always introduced by a revision note that appears first under the
heading of the class affected. (There are no new schedule, complete revision, or
extensive revision notes in Abridged Edition 15.)
7.22 Discontinued notes indicate that all or part of the contents of a number have
been moved to a more general number in the same hierarchy, or have been
dropped entirely. For example:
354[.2] General considerations of administration
Number discontinued; class in 354

xlii
 Introduction

748.2 Blown, cast, decorated, fashioned, molded, pressed glass

Use of this number for glassware discontinued; class in 748
7.23 Relocation notes state that all or part of the contents of a number have been
moved to a different number. For example:
[018] Catalogs arranged by author, main entry, date, or register number
Relocated to 017
398 Folklore
Interdisciplinary works on chapbooks relocated to 002
The former number is usually given at the new number, either in the heading or
in the appropriate note. For example:
002 The book
Including interdisciplinary works on chapbooks [ formerly 398]
017 General bibliographies and catalogs of works held in specific
collections or offered for sale
Class here catalogs arranged by author, main entry, date, or
register number [ formerly 018], ...
7.24 Do-not-use notes instruct the classifier not to use all or part of the regular stan-
dard subdivision notation, but instead to use a special provision or standard
subdivision notation at a broader number. When the whole standard subdivision
is removed from use, the note appears under a bracketed standard subdivision;
when only part of the standard subdivision is displaced, the part displaced is
specified. For example:
259[.09] History, geographic treatment, biography
Do not use; class in 253.09
337.109 History and biography
Do not use for geographic treatment; class in 337.1

Number Building
8.1 The classifier will often find that to arrive at a precise number for a work it is
necessary to build or synthesize a number that is not specifically listed in the
schedules. Such built numbers allow for greater depth of content analysis. They
are used only when instructions in the schedules make them possible (except
for standard subdivisions, which are discussed in paragraphs 8.3–8.11). Number
building begins with a base number (always stated in the instruction note) to
which another number or notation is added.

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 Dewey Decimal Classification

8.2 There are four sources of notation for building numbers: (A) Table 1 Standard
Subdivisions; (B) Tables 2–4; (C) other parts of the schedules; and (D) add
tables in the schedules.
(A) Adding Standard Subdivisions from Table 1
8.3 A standard subdivision represents a recurring physical form (such as a diction-
ary, periodical, or index) or approach (such as history or research) and thus is
applicable to any subject or discipline that covers or approximates the whole of
the meaning of the number. Here are a few examples with the standard subdivi-
sion concept underlined (in some cases an extra 0 precedes the standard subdi-
vision according to instructions found in the schedules):
150.1 Philosophy and theory of psychology
230.003 Dictionary of Christianity
340.025 Directory of lawyers
405 Periodical on language
507.8 Use of apparatus and equipment in the study and teach-
ing of science, e.g., science fair projects
624.0285 Computer applications in civil engineering
796.812092 Biography of a wrestler
808.0071 Teaching of rhetoric
Further instructions on using Table 1 are found at the beginning of Table 1. See
also Manual notes on selected standard subdivisions.
8.4 Standard subdivisions are not usually listed in the schedules except where
needed to fill out three-digit numbers, e.g., 605 Serial publications, and in a few
other instances. Standard subdivisions may be listed in the schedules when the
subdivisions have extended or narrowed meanings. For example:
580.75 Museum activities and services (extended meaning)
Including preserving botanical specimens
390.088 [Customs of] Religious groups (narrowed meaning)
Do not use for occupational groups; class in 390
Standard subdivisions may also be listed to introduce an expansion featuring
special notation (the subdivisions in the expansion are not standard subdivi-
sions). Such standard subdivisions are accompanied by a special note. For exam-
ple:
370.1 Philosophy and theory, education for specific objectives,
educational psychology
Notation 01 from Table 1 as modified below
Sometimes, standard subdivisions are listed because references to other classes
or the Manual are required. For example:

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 Introduction

507.2 Research
Class research covering the sciences in the broad sense
of all knowledge, scientific method as a general research
technique in 001.4
See Manual at 500 vs. 001
8.5 When standard subdivision notation from Table 1 is listed in Tables 2–4 and in
the schedules, all of the notation’s notes and subdivisions as given in Table 1 are
applicable unless other instructions are given. Other Table 1 notation that is not
listed in the schedules may also be used. For example, the fact that 610.7 is listed,
but not 610.8 or the subdivisions of 610.7, does not exclude the use of 610.8 or
610.71.
8.6 Notation from Table 1 Standard Subdivisions may be added to any number in
the schedules unless there is a specific instruction to the contrary. The classifier
should never use more than one zero in applying a standard subdivision unless
instructed to do so. If more than one zero is needed, the number of zeros is
always indicated in the schedules. When using standard subdivisions with num-
bers built by adding from Tables 2–4 or other parts of the schedules, be sure to
check the table or schedule used for the segment preceding the standard subdi-
vision for special instructions on the number of zeros.
8.7 The most important caveat with respect to standard subdivisions is that they are
added only for works that cover or approximate the whole of the subject of the
number. For example, a work on the management of educational voucher pro-
grams should be classed in 379.3, not 379.3068. Notation 068 from Table 1 may
not be added to 379.3 because educational vouchers are in an including note at
379.3; therefore, educational vouchers do not approximate the whole of the sub-
ject of the number.
8.8 Standard-subdivisions-are-added notes indicate which topics in a multiterm
heading may have standard subdivisions added for them because the designated
topics are considered to approximate the whole of the subject. For example:
371 Schools and their activities; special education

Standard subdivisions are added for schools and their activities,
special education together; for schools and their activities together;
for schools alone
Standard-subdivisions-are-added notes do not have hierarchical force beyond
the standard subdivisions associated with the number itself. For example, the
note under 371 governs the application of standard subdivisions to 371 itself,
but not to 371.1–371.9.
8.9 Do not add multiple standard subdivisions to the same number except when
specifically instructed to do so, and in the following instances. Standard sub-
divisions may be added to subdivisions of —04 Special topics that are specifi-

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 Dewey Decimal Classification

cally listed in the schedules. For example, standard subdivisions may be added
to 621.044 Plasma engineering, a subdivision of 621.04 Special topics of applied
physics.
Standard subdivisions may also be added to special notation in the regular stan-
dard subdivision sequence. For example, under 370.1, there is an expansion for
educational objectives at 370.11 Education for specific objectives. Standard sub-
divisions may be added to 370.11 and its subdivisions, since 370.11 and its sub-
divisions are special notation.
Standard subdivision concepts may be displaced to a special provision in the-
regular sequence of standard subdivisions or elsewhere; in either case, standard
subdivisions may be added to the special provision. For example, the standard
subdivision concept “testing and measurement” has been displaced from 370.28
Auxiliary techniques and procedures to 371.26 Examinations and tests; academic
prognosis and placement. Notation 03 from Table 1, the standard subdivision for
encyclopedias, may be added to 371.26 Examinations and tests; academic prog-
nosis and placement to represent an encyclopedia of educational testing 371.2603.
The full range of standard subdivisions may also be added to standard sub-
division concepts displaced to notation outside the regular sequence of stan-
dard subdivisions, e.g., directory of social service agencies in Great Britain
361.941025 (history, geographic treatment, biography has been displaced from
361.009 to 361.9).
8.10 In many places in the schedules, there are numbers outside the regular sequence
of standard subdivisions that look like standard subdivisions but are not stan-
dard subdivisions. If additional subdivisions are intended to be used at the
special provision, an add note is provided. For example, at 027.009, a regular
standard subdivision, geographic treatment is displaced to 027.01–027.09:
027.009 History and biography
Do not use for geographic treatment; class in
027.01–027.09
027.01–027.09 *Geographic treatment
Add to base number 027.0 notation 1–9 from Table 2,
e.g., libraries in France 027.044
The special provision for geographic treatment at 027.01–027.09 is not a stan-
dard subdivision. If appropriate, standard subdivisions may be added to the
resulting notation, e.g., an encyclopedia of libraries in France 027.04403.
8.11 Standard subdivisions should not be used where redundant, i.e., where the subdi-
vision means the same as the base number, or where application of the standard
subdivision would needlessly segregate material by aspects not emphasized by
the author. Special care should be taken in adding standard subdivisions to built
numbers, since the standard subdivision applies to the whole number and not
just to part of the number.

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 Introduction

(B) Adding from Tables 2–4

8.12 The classifier may be instructed to add notation from Tables 2–4 to a base num-
ber from the schedules or to a number from a table. A summary of the use of
each table follows. Further instructions on using Tables 2–4 are found at the
beginning of each table. See also the Manual notes for Tables 2–4.
8.13 Table 2 Geographic Areas, and Biography. The major use of Table 2 is with
notation 09 from Table 1, where it can be added to every number in the sched-
ule unless there are specific instructions to the contrary. For example, read-
ing instruction in the primary schools of Australia is 372.40994 (372.4 reading
instruction in primary schools + 09 History, geographic treatment, biography
from Table 1 + 94 Australia from Table 2).
8.14 Area notation is sometimes added directly to schedule numbers, but only when
specified in a note. For example:
373.3–373.9 Secondary education in specific continents, countries, localities
Add to base number 373 notation 3–9 from Table 2, e.g.,
secondary schools of Australia 373.94
8.15 Table 3 Subdivisions for Individual Literatures, for Specific Literary Forms.
These subdivisions are used in class 800 as instructed, usually following num-
bers for specific languages in 810–890.
8.16 Table 4 Subdivisions of Individual Languages and Language Families. These
subdivisions are used as instructed in class 400, following numbers for desig-
nated specific languages or language families in 420–490.
(C) Adding from Other Parts of the Schedules
8.17 There are many instructions to make a direct addition to a number from another
part of the schedules. For example:
016 Bibliographies and catalogs of works on specific subjects
Add to base number 016 notation 001–999, e.g., bibliographies
of computer programs and software 016.0053, of general
encyclopedic works 016.03, of philosophy 016.1, of novels
016.80883, of general collected biographies 016.92
In this example, the 0053 in 016.0053 comes from 005.3 Programs, the 03 in
016.03 comes from 030 General encyclopedic works, the 1 in 016.1 comes from
100 Philosophy (note that the final zeros are dropped from the end of the num-
ber), the 80883 in 016.80883 comes from 808.83 Collections of fiction, and the
92 in 016.92 comes from 920 Biography, genealogy, insignia (note that the final
zero is dropped from the end of the number).
8.18 In many cases, part of a number may be added to ­another number upon instruc-
tion. For example:

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 Dewey Decimal Classification

636.9 Other mammals

Add to base number 636.9 the numbers following 599 in
599.2–599.8, e.g., rodents 636.935, fur-bearing animals
636.97 ...
In this example, 35 comes from 599.35 Rodents, and 7 comes from 599.7 Carni-
vores, where the topic “fur-bearing animals” appears as a class-here note.
(D) Adding from Tables Found in the Schedules
8.19 Add tables in the schedules provide numbers to be added to designated sched-
ule numbers (identified by a symbol and accompanying footnoted instruction);
these tables must be used only as instructed. For example:
384.54 *Radiobroadcasting
The asterisk in the entry above leads to the following footnote: “Add as instructed
under 380.” The add table at 380 is used only for headings tagged with an aster-
isk or for topics in class‑here notes under headings tagged with an asterisk.
8.20 Subdivisions-are-added notes indicate which terms in a multiterm heading may
have subdivisions applied to them. For example:
672 Iron, steel, other iron alloys
Add to base number 672 the numbers following 671 in 671.2–671.8,
e.g., welding 672.5
Subdivisions are added for any or all topics in heading

Citation and Preference Order

9.1 Citation and preference order must be considered when multiple aspects or char-
acteristics of a subject (such as age, area, gender, historical periods, national
origin) are provided for in the Classification, and a single work treats more than
one of them.

Citation Order
9.2 Citation order allows the classifier to build or synthesize a number using two
or more characteristics ( facets) as specified in instruction notes. Success in
building a DDC number requires determining which characteristics apply to a
specific work, and then determining from the instructions in the schedule the
sequence in which the facets will be ordered.
9.3 The notes at the beginning of Table 3 are an example of number-building
instructions that specify the sequence in which characteristics of literature (if
applicable) will be shown: first language; then literary form; then standard sub-
divisions, or collections, or history, description, critical appraisal.

xlviii
 Introduction

P reference Order
9.4 If there is no provision to show more than one of the aspects or characteristics,
it is a matter of preference (because a choice must be made among several char-
acteristics). Preference notes supply either an instruction or table establishing
the order in which to make the choice. An example of a preference instruction
is found at 571–575:
571–575 Internal biological processes and structures
Unless other instructions are given, class a subject with
aspects in two or more subdivisions of 571–575 in the
number coming last, e.g., cytology of animal circulatory
system 573.1 (not 571.1 or 571.6)
9.5 An example of a table indicating preference order is found at 302–307:
> 302–307 Specific topics in sociology and anthropology
Unless other instructions are given, observe the following table of
preference, e.g., friendship among women 302.34082 (not 305.4):
Factors affecting social behavior 304
Social processes 303
Social interaction 302
Culture and institutions 306
Groups of people 305
Communities 307

The Manual
10.1 The Manual gives advice on classifying in difficult areas, and provides guid-
ance on choosing between related numbers.
10.2 See-Manual references in the schedules and tables refer the classifier to the
Manual for additional information about a certain number, range of numbers,
or choice among numbers. In some cases, the see-Manual reference refers only
to a portion of a longer Manual note, or topic narrower than the numbers in the
heading, e.g., “See Manual at 930–990: Historic preservation.” The see-Manual
reference is repeated in the entries for each of the numbers or number spans cov-
ered in the Manual note. For example, “See Manual at 004.6 vs. 621.382, 621.39”
is listed in the entries for 004.6, 621.382, and 621.39.
10.3 Brief Manual-like notes are sometimes given directly in the schedule or table
entry. For example:
640 Home and family management

Use 640 for housekeeping covering activities related to running
the home, e.g., preparing meals and doing routine repairs as well
as cleaning. Use 648 for housekeeping limited to cleaning

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 Dewey Decimal Classification

A rrangement and Format of the M anual

10.4 The Manual is arranged by table and schedule numbers, with the broadest span
coming before entries for narrower spans or individual numbers. Manual notes
are entered under the preferred or “if-in-doubt” number. If there is no if-in-
doubt number, prefer the interdisciplinary number.
10.5 The Manual note heading summarizes the contents of the note. The terms in
the Manual note headings need not match the terms associated with the same
number(s) in the tables and schedules if the note is narrower than the number, or
the note refers to more than one number. For example:
T1—01
Philosophy and theory
T1—01 vs. T1—02
Scientific principles vs. The subject for people in scientific and
technological occupations
10.6 If the Manual note is very long, or part of the note focuses on a topic narrower
than the heading, subheadings may be provided. For example:
T1—068 vs. 353–354
Public administration and management in specific fields
Exceptions (subheading)

The Relative Index

11.1 The Relative Index is so named because it relates subjects to disciplines. In
the schedules, subjects are distributed among disciplines; in the Relative Index,
subjects are arranged alphabetically, with terms identifying the disciplines in
which they are treated subarranged alphabetically under them. For example:
Clothing 391
armed forces 355.8
arts 746.9
commercial manufacturing 687
customs 391
home economics 646
home sewing 646.4
product safety 363.19
psychological influence 155.9
see Manual at 391 vs. 646, 746.9
In some cases the term implies rather than states the discipline. In the example
above, the discipline of home economics is listed, but the discipline of military
science is implied by “armed forces.”

l
 Introduction

11.2 The Relative Index is primarily an index to the DDC as a system. It includes
most terms found in the schedules and tables, and terms with literary war-
rant for concepts represented by the schedules and tables. The Relative Index
is not exhaustive. If the term sought is not found, the classifier should try a
broader term, or consult the schedules and tables directly. The schedules and
tables should always be consulted before a number found in the Relative Index
is applied.
A rrangement and Format of the R elative I ndex
11.3 Index entries are arranged alphabetically word by word, e.g., Birth order pre-
cedes Birthdays. Entries with the same word or phrase but with different marks
of punctuation are arranged in the following order:
Term
Term. Subheading
Term (Parenthetical qualifier)
Term, inverted term qualifier
Term as part of phrase
Initialisms and acronyms are entered without punctuation and are filed as if
spelled as one word. Hyphens are ignored and treated as a space. Terms indented
below the main headings are alphabetized in one group even though they may
be a mixture of disciplines, topical subheadings, and, to a limited extent, words
that form phrases or inverted phrases when combined with the main heading.
11.4 Class numbers are listed in groups of three digits for ease of reading and copy-
ing. The spaces are not part of the numbers and do not represent convenient
places to abridge the number.
11.5 See‑also references are used for synonyms and for references to broader terms
(but only when three or more new numbers will be found at the synonym or
broader term), and for references to related terms (which may provide only one
or two new numbers).
11.6 See-Manual references lead the classifier to relevant discussions in the Manual.
11.7 Numbers drawn from Tables 1–4 are prefixed by T1 through T4. (For a complete
listing of table names and abbreviations, see paragraph 7.4.)

I nterdisciplinary Numbers
11.8 The first class number displayed in an index entry (the unindented term) is the
number for interdisciplinary works. If the term also appears in a table, the table
number is listed next, followed by other ­aspects of the term. The discipline of
the interdisciplinary number may be repeated as a subentry if the discipline is
not clear. For example:

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 Dewey Decimal Classification

Oceans 551.46
T2—162
biology 578.77
ecology 577.7
law of nations 341.4
physical geology 551.46
resource economics 333.91
see Manual at T2—162
11.9 Interdisciplinary numbers are not provided for all topics in the Relative Index.
They are omitted when the index entry is ambiguous, does not have a disciplin-
ary focus, or lacks literary warrant. In such cases, there is no number opposite
the unindented entry. For example:
Proof theory
mathematical logic 511.3
(For more information on interdisciplinary numbers, see paragraphs 5.8, 7.16,
7.18–7.19.)

Terms I ncluded in the R elative I ndex

11.10 The Relative Index contains most terms found in the headings and notes of the
schedules and tables, and synonyms and terms with literary warrant for con-
cepts represented by the schedules and tables. The Relative Index also contains
terms for the broad concepts covered in Manual notes.
Inverted phrases are avoided, except for personal and geographic names (see
paragraphs 11.12–11.13). Qualifiers are used for homonyms, ambiguous terms,
and most initialisms and abbreviations. The most common use of the term may
not be qualified. Disciplinary qualifiers are avoided.
11.11 The following types of names from Table 2 Geographic Areas are included in
the Relative Index: (A) names of countries; (B) names of the states and prov-
inces of several countries; and (C) names of certain important geographic fea-
tures.
11.12 Also included in the Relative Index are the personal names of the following
groups of persons: heads of state used to identify historical periods, e.g., Abra-
ham Lincoln; and founders or revealers of religions, e.g., Muḥammad.
11.13 Place names and other proper names are generally given in the form specified
by the second edition, 2002 revision, 2005 update, of the Anglo‑American Cata-
loguing Rules (AACR2), based on the names established in the Library of Con-
gress authority files. If the AACR2 form is not the common English name, an
entry is also included under the familiar form of the name.
Plants and animals are indexed under their common names.
11.14 The choice of singular form versus plural form follows ISO 999:1996, Guide-
lines for the content, organization and presentation of indexes. Count nouns are

lii
 Introduction

generally in the plural; noncount nouns and abstract concepts are generally in
the singular. Parts of the body are in the plural only when more than one occurs
in a fully formed organism (e.g., ears, hands, nose). Plants and animals follow
scientific convention in the choice of singular form versus plural form, with the
decision based on whether the taxonomic class has more than one member (e.g.,
Dogs, Lion, Yorkshire terrier). Where usage varies across disciplines, the index
entry reflects the form preferred in the discipline where interdisciplinary works
are classified.
Terms Not I ncluded in the R elative I ndex
11.15 Terms usually not included in the Relative Index are:
(A) Phrases beginning with the ­ adjectival form of countries, languages,
nationalities, religions, e.g., English poetry, French cooking, Italian
architecture, Hindu prayer books.
(B) Phrases that contain general concepts represented by standard subdivi-
sions such as education, statistics, laboratories, and management; e.g.,
Art education, Educational statistics, Medical laboratories, Bank man-
agement.
When there is strong literary warrant for such a phrase heading as a sought
term, it may be included in the Relative Index, e.g., English literature. When the
phrase heading is a proper name or provides the only form of access to the topic,
it may also be included, e.g., French horns.

Options
12.1 Some devices are required to enable the DDC to serve needs beyond those
represented in the standard English-language edition. At a number of places in
the schedules and tables, options are provided to give emphasis to an aspect in
a library’s collection not given preferred treatment in the standard notation. In
some cases, options are also suggested to provide shorter notation for the aspect.
12.2 Options are provided throughout the Classification to emphasize jurisdiction,
ethnic or national group, language, topic, or other characteristic.
12.3 Options described in notes appear in parentheses and begin with “Option:”.
Options that apply to the full entry appear at the end of the entry; options to
a specific instruction in the entry are indented under the appropriate note. For
example, the following option appears indented under a note in the entry for
810–890:
(Option: Class translations into a language requiring local emphasis
with the literature of that language)
12.4 Some optional numbers are enumerated in the schedules and tables and appear
in parentheses in the number column.
12.5 Arrange-alphabetically and arrange-chronologically notes are not placed in
parentheses, but are also options. They represent suggestions only; the mate-

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 Dewey Decimal Classification

rial need not be arranged alphabetically or chronologically. An example of an

­arrange-alphabetically note is found at 005.265 Programming for specific com-
puters: “Arrange alphabetically by name of computer, e.g., Apple iMac®.”
12.6 Some national libraries and central cataloging authorities assign a few optional
numbers, e.g., Library and Archives Canada uses C810 for Canadian literature
in English and C840 for Canadian literature in French.
12.7 Most of the time, the responsibility for implementing an option rests with the
local library. Libraries should weigh the value of using an option against the
loss in interoperability of numbers. The library will not be able to use numbers
assigned by other libraries, and other libraries will not be able to use the optional
numbers assigned by the library. In addition, unless the option is widely used in
a region, users may be confused by the alternate notation.

Close and Broad Classification

13.1 The Dewey Decimal Classification provides the basic option of close versus
broad classification. Close classification means that the content of a work is
specified by notation to the fullest extent possible. Broad classification means
that the work is placed in a broad class by use of notation that has been logically
abridged. For example, a work on French cooking is classed closely at 641.5944
(641.59 Cooking by place + 44 France from Table 2), or broadly at 641.5 (Cook-
ing).
13.2 A library should base its decision on close versus broad classification on the size
of its collection and the needs of its users. For example, an engineering library
might prefer close classification for works in engineering, but broad classifica-
tion for disciplines outside science and technology.
13.3 The classifier should never reduce the notation to less than the most specific
three‑digit number (no matter how small the library’s collection). A number
also must never be reduced so that it ends in a 0 anywhere to the right of the
decimal point.
13.4 One aid to logical abridgment of DDC numbers is the segmentation device pro-
vided by the Dewey Section of the Library of Congress and some other central-
ized cataloging services.

More Information
14.1 Classifiers desiring a more in‑depth introduction to the Dewey Decimal Classi-
fication may consult Dewey Decimal Classification: Principles and Application,
3d ed., by Lois Mai Chan and Joan S. Mitchell (Dublin, Ohio: OCLC, 2003).
14.2 More information about the use and application of the DDC, plus training mate-
rials, can be found on the Dewey web site (http://www.oclc.org/dewey/) and on
025.431: The Dewey blog (http://ddc.typepad.com/).

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