These are some definitions and principles taken from S.R. Ranganathan’s Prolegomena to Library Classification (2e) (1957). The terminology isn’t easy to crack without some examples, but just keep in mind that he’s talking about how classification schemes like the Dewey and Library of Congress systems work. They organize knowledge (in books and other things) by deciding what the book is about and then giving it a call number and putting it in order with other books. How that aboutness is decided, to what level of detail, and how the call numbers are made, is what he’s discussing. He’s setting out the basic rules he thinks all classification schemes should use. (He thought of them while working on his own system, Colon Classification.) Dividing “Mammals” with “Cats” and “Dogs” makes a lot more sense than dividing “Whiskered Animals” into “Ones that Meow” and “Ones that Bark,” for example—but why exactly? Should cats come before dogs—why or why not? The definitions below are all verbatim from the book, and anything I added is in square brackets.
A Characteristic is any attribute of any complex of attributes with reference to which the likeness or unlikeness of entities can be determined and at least two of them are unlike. [E.g. height is a characteristic of boys, but not possession of a face, which is an attribute shared equally by all boys.]
A Class is a ranked group. [If a set of things is divided into groups based on characteristics or attributes, and those groups are ranked, then each ranked group is a class. Q (Science) in LC is a class, as is Philosophy and Psychology (100s) in Dewey.]
An Array is the sequence of the classes of a universe, derived from it on the basis of a single characteristic and arranged among themselves according to their ranks. [Ranked groups making classes form an array of the first order. The ten main classes in Dewey form an array, as are the letters in LC.]
118: Chain of Classes
A set of classes such as 3, 32, 322, 3221, having lineal kinship, so to speak, is a Chain of Classes. Class 3 is the First Link of the Chain, class 3221 is the Last Link. [Another example: Universe of Knowledge -> Social Sciences -> Economics -> Labour -> Labouring classes -> Duration of work.]
Canons for Characteristics
131: Canon of Differentiation
Each characteristic used should differentiate, that is, it should give rise to at least two classes.
132: Canon of Concomitance
No two characteristics should be concomitant.
133: Canon of Relevance
Each characteristic should be relevant to the purpose of the classification.
134: Canon of Ascertainability
Each characteristic should be definitely ascertainable.
135: Canon of Permanence
Each characteristic should continue to be both ascertainable and unchanged, so long as there is no change in the purpose of the classification.
136: Canon of Relevant Sequence
The characteristics of the scheme are to be used in a sequence relevant to the purpose of the classification.
137: Canon of Consistency
The sequence of applying the chosen characteristics should be consistently adhered to.
Canons for Array
141: Canon of Exhaustiveness
The classes in any array of classes should be totally exhaustive of their common immediate universe.
142: Canon of Exclusiveness
The classes in an array of classes should be mutually exclusive.
143: Canon of Helpful Sequence
The sequence of the classes in any array should be helpful. It should be according to some convenient principle, and not arbitrary, wherever insistence on one principle does not violate other more important requirements.
144: Canon of Consistent Sequence
Whenever similar classes occur in different arrays, their sequences should be parallel in all such arrays, wherever insistence on such a parallel does not run counter to other more important requirements. (See Principles for Helpfulness in Array below.)
Canons for Chain
151: Canon of Decreasing Extension
While moving down a chain from its first link to its last link, the intension of the classes should increase, and the extension of the classes should decrease.
152: Canon of Modulation
A chain of classes should comprise one class of each and every order that lies between the orders of the first link and the last link of the chain.
Canons for Filiatory Sequence
161: Canon for Subordinate Clauses
All the subordinate classes of a class, in whatever chain they may occur, should immediately follow it, without being separated from it or among themselves by any other class.
162: Canon for Co-ordinate Classes
Among the classes in an array, no class with less affinity should come between two classes with greater affinity.
Canons for Terminology
171: Canon of Currency
Each of the terms used to denote the classes in a scheme of classification must be the one currently accepted by those specialising in the universe to which the scheme is applicable.
172: Canon of Reticence
The terms used to denote the classes in a scheme of classification should not be critical.
173: Canon of Enumeration
The denotation of each term in a scheme of classification should be decided in the light of the classes enumerated in the various chains (lower links) having the class denoted by the term as their common first link.
174: Canon of Context
The denotation of each term in a scheme of classification should be decided in the light of the different classes of lower order (upper links) belonging to the same primary chain as the class denoted by the term.
Canons for Notation
1881: Canon of Relativity
The length of a class number in a scheme of classification should be proportional to the order of the intension of the class it represents.
1882: Canon of Expressiveness
A class number should be expressive of the relevant characteristics of the class represented by it.
1883: Canon of Mixed Notation
The notation of a scheme of classification should be mixed.
Special Canons for Knowledge Classification
221: Canon of Hospitality in Array
The construction of a class number should admit of an infinite number of new co-ordinate class numbers being added to an array without disturbing the existing class numbers in any way.
231: Canon of Hospitality in Chain
The construction of a new class number should admit of an infinity of new class numbers being added at the end of its chain without disturbing any of the existing class numbers in any way.
241: General Canon of Mnemonics
The digit or digits used to represent a specified concept in a class number should be the same in all class numbers having the concept represented in them, provided that insistence on such consistent representation does not violate more important requirements.
252: Canon of Verbal Mnemonics
Verbal mnemonics should be rejected, without any hesitation, if a sequence more helpful to readers or more filiatory than alphabetical sequence exists. Verbal mnemonics by alphabetical device should be preferred if the alphabetical sequence is as helpful as any other sequence. The word forming the basis of verbal mnemonics should be that of international nomenclature whenever it has been set up.
261: Canon of Scheduled Mnemonics
A scheme of classification should include a preliminary set of schedules of divisions based on characteristics likely to recur in a array of some order or other of all or many classes, or refer any recurrent array of divisions to the one schedule of them giving in connection with an appropriate class.
271: Canon of Seminal Mnemonics
A scheme of classification should use one and the same digit to denote seminally equivalent concepts in whatever array of whatever class they may appear.
Special Canons for Book Classification
621: Canon of Classics
A Scheme of Book Classification should have a device to bring together all the editions, translations, and adaptations of a classic, and next to them all the editions, etc., of the different commentaries on it, the editions, etc., of a particular commentary all coming together, and next to each commentary all the editions, etc., of the commentaries on itself in a similar manner (commentaries of the second order), and so on.
631: Canon of Local Variation
The notational system of a scheme of book classification should provide for variations due to special interests.
662: Canon of Book Number
A scheme of book classification should be provided with a scheme of book numbers to individualise the documents having the same class of knowledge as their ultimate class.
678: Canon of Collection Number
A Scheme of Book Classification may be provided with a Schedule of Collection Numbers to individualise the various collections of special documents to be formed on the basis of the peculiarities of their gross bodies, or their rarity, or service exigency to facilitate use by readers. The collection numbers based on physical peculiarity may be of use in bibliographies also.
6852: Canon of Distinctiveness
In a Scheme of Library Classification, the class number, the book number, and the collection number, together forming the call number, should be written quite distinct from one another.
3581: Principle of Increasing Concreteness
If two classes are such that one can be said to be more abstract and less concrete than the other, the former should precede the latter.
3582: Principle of Increasing Artificiality
If two classes are such that one can be said to be nearer to the “thing-in-itself” or naturalness and farther from artificiality than the other, the former should precede the other.
For Facet Formula
3583: Principle of Inversion
In an analytico-synthetic classification, the implementation of the Principle of Increasing Concreteness requires that the facets in the facet formula of a basic class should be in the decreasing sequence of concreteness. If the scheme has rounds of facets, the facets in each round should be in the decreasing sequence of concreteness.
For Helpfulness in Array
1431: Principle of Increasing Quantity
If the characteristic used admits of quantitative measurement, the sequence of the classes may be in the ascending sequence of the measure in which the classes share the characteristic.
1432: Principle of Later-in-Time
If the classes in an array have originated in different times, they may be arranged in a parallel progressive time-sequence.
1433: Principle of Later-in-Evolution
If the characteristic is of an evolutionary nature, the sequence of the classes may be parallel to the course of evolution.
1434: Principle of Spatial Continuity
If the classes of an array occur contiguously in space, they may be arranged in a parallel spatial sequence.
1435: Principle of Increasing Complexity
If the classes in an array show different degrees of complexity, they are arranged in the sequence of increasing complexity.
1436: Principle of Canonical Sequence
If the classes are traditionally referred to in a specific sequence, although no underlying principle is discoverable, it will be convenient to confirm to this traditional sequence.
1437: Principle of Favoured Category
The classes in an array may be arranged in the sequence of the decreasing quantity of published documents on them.
1438: Principle of Alphabetical Sequence
When no other sequence of the classes in an array is more helpful, they are arranged alphabetically by their names current in international usage.