1- Plato (c.370 BC)
"Socrates: That of dividing things again by classes, where the natural joints are, and not trying to break any part, after the manner of a bad carver." (Plato c.370 BC, Phaedrus 265e).
2- Aristotle (350 BCE, Book I, chap. 1, part 5)
"A 'genus' is what is predicated in the category of essence of a number of things exhibiting differences in kind. We should treat as predicates in the category of essence all such things as it would be appropriate to mention in reply to the question, 'What is the object before you?'; as, for example, in the case of man, if asked that question, it is appropriate to say 'He is an animal'" (Aristotle 350 BCE, Book I, chap. 1, part 5). Note: "The logic of classifications, which remains, in this time, the Aristotelian logic, receives practically no new development until the 18th century" (Parrochia 2016; electronic source, no pages; see also Sutcliffe 1993).
3- Michel Adanson (1763, clvi)
"...all parts and qualities, or properties and faculties of plants... barring not even one" ought to be considered before attempting a classification.
4- David Cranz (1767, vol. 1, ix)
"I have described what belongs to this science, not according to the classifications [Ger. Eintheilungen] and characteristics, which are generally adopted by, and needful for the modern naturalists, but according to a certain affinity or likeness."
5- Carl Linnaeus (1767, p. 152)
"Natura Insectorum per plures eorum ætates jam perspecta, superest ut systematice eadem contemplemur. Recta autem eorum CLASSIFICATIO vitam huic scientiæ & facultatem conciliat, ubi singula insecta suum quasi nomen ipsa produnt" = "The nature of insects through their several ages [stages of life] having already been examined, it remains to contemplate them systematically. Now the correct CLASSIFICATION of them [sci., insects] furnishes life and means to this science, where individual insects themselves produce, as it were, their own name." (majuscule in original).
6- Thomas Reid (1785, p.191)
"Our ability to distinguish and give names to the different attributes belonging to a single thing goes along with an ability to observe that many things have certain attributes in common while they differ in others. This enables us to put the countless hordes of individuals into a limited number of classes, which are called 'kinds' and 'sorts' - and in the scholastic language called 'genera' and 'species'" (here quoted from Frické 2012, 25).
7- William Whewell (1840, vol. 1, xxxiii, XCV)
"The attempts at Natural Classification are of three sorts; according as they are made by the process of blind trial, of general comparison, or of subordination of characters. The process of Blind Trial professes to make its classes by attention to all the characters, but without proceeding methodically. The process of General Comparison professes to enumerate all the characters, and forms its classes by the majority. Neither of these methods can really be carried into effect. The method of Subordination of Characters considers some characters as more important than others; and this method gives more consistent results than the others. This method, however, does not depend upon the Idea of Likeness only, but introduces the Idea of Organization or Function" (italics in original).
8- John Stuart Mill (1843, vol. 2, Bk. IV, Ch. 7, p.299-300)
"Classification, thus regarded, is a contrivance for the best possible ordering of the ideas of objects in our minds; for causing the ideas to accompany or succeed one another in such a way as shall give us the greatest command over our knowledge already acquired, and lead more directly to the acquisition of more. The general problem of Classification, in reference to these purposes, may be stated as follows: To provide that things shall be thought of in such groups, and those groups in such an order, as will best conduce to the remembrance and to the ascertainment of their laws."
9- William Benjamin Carpenter (1847, I. §2)
"The object of all Classification ... [is] to bring together those beings which most resemble each other and to separate those that differ."
10- Charles Darwin (1859, p.420)
"... all true classification is genealogical ..." (See also Mayr and Bock 2002; Padian 1999.).
11- Thomas Henry Huxley (1869, p. 1)
"By the classification of any series of objects is meant the actual, or ideal, arrangement together of those which are like and the separation of those which are unlike, the purpose of this arrangement being to facilitate the operation of the mind in clearly conceiving and retaining in the memory, the characters of the objects in question."
12- Charles Ammi Cutter (1876, p.10)
"Class, a collection of objects having characteristics in common".
13- Robert Adamson (1901, v.1, p.185)
"The process of arranging the objects of some province of experience into kinds or groups, characterized by the possession of common marks. As ordinarily defined, it involves more than logical DIVISION (q.v.), the rules of which furnish the minimal conditions of the process. In addition, classification takes into account (1) either the specific purpose of the arrangement, or (2) the natural conjunctions of marks which are of most importance. In either case, the aim of classification is to render possible the greatest number of general propositions regarding the objects, and so to facilitate the complete and systematic survey of them. The ideal of a classification that is not determined by special, human ends, as e.g. in classification of occupations in a census return, is to copy in its systematic arrangement the real order of interdependence in the things themselves. What is called 'artificial,' as opposed to natural classification, differs in degree only, not in kind. Literature: MILL, Logic, Bk. IV. chaps. vii, viii; VENN, Empirical Logic, chap. xxx; JEVONS, Princ. of Sci., chap. xxx. (R.A.)."
14- Ernest Cushing Richardson (1901, p.1)
Classification is the "putting together of like things, or more fully described, it is the arranging of things according to likeness and unlikeness. It may also be expressed as the sorting and grouping of things. It is convenient sometimes, to speak of ‘likeness and unlikeness' but really in classification it is 'likeness' which rules while 'unlikeness' is merely what is left over when likeness has been defined. The 'putting together of like things' is therefore the fullest and most exact form of the definition."
15- Henry E. Bliss (1935, p.3)
"In dealing with the multiplicity of particular things, actualities, and specific kinds, we find that some are alike, in general characters and in specific characteristics; and we may consequently relate them in a class, or classes, that is classify them."
16- Jason E. L. Farradane (1950, p.83,p. 87) (1952,p. 73-74)
"Classification is a theory of the structure of knowledge, i.e. of the relations between different parts of knowledge. No arbitrary method of grouping, however carefully applied, is true classification. The problem is primarily epistemological. What is true knowledge, and what are true relations between the parts of knowledge? It is essential to define these if the classification is to be true and logically sound." "A classification indicates the relations between items of knowledge." "A classification represents a theory of the structure of knowledge, i.e. of the relations between the different parts of knowledge. The basic problem is to determine what these relations are and how they link the different concepts from our knowledge into a coherent structure. The arbitrary or 'deductive' subdivision of an assumed total of knowledge cannot give a true representation of these relations, which do not consist only of groupings of a class and its members, or division of a whole into its parts. It was shown that a classification must be constructed 'inductively', or upwards, piecing together known fragments of relations."
17- Jesse H. Shera (1965, p. 120,p. 127)
"Classification is the crystallization or formalizing of inferential thinking, born of sensory perception, conditioned by the operation of the human brain, and shaped by human experience. It lies at the foundation of all thought, but it is pragmatic and it is instrumental." "He [the librarian] must appreciate classification, not as a tool, but as a discipline in which is to be studied the reaction and response of a living mind to the record left by a distant and usually unknown mind; a discipline that seeks to achieve a better understanding of the changing patterns of thought and the points of contact at which they can be related to specific units of recorded information."
18- Shiyali Ramamrita Ranganathan (1967, Chapter CP, 77-78)
Ranganathan distinguished five senses of 'classification'. 1. "Division. (See Chap CC). This is the primitive meaning of the term 'classification'. Even a child practises classification in Sense 1 with its playthings. Even early man had practised it. 2. Assortment [grouping of things of the same sort]. (See Chap CD). Classification in Sense 2 is inherent in Man. Perhaps it is a concomitant of the finiteness of the speed of neural impulses in the human body. When the speed is finite, structure emerges. Wherever there is a structure, sequences emerge. When sequence is helpful to the purpose at hand, it is Classification. The sequence inevitable inside of the skin, so to speak, gets expressed extraneurally also. To classify in Sense 2 is thus a neural necessity. Sharpness in thinking, clarity in expression, unerringness in communication, expedition in response, and exactness in service depend ultimately on helpful sequence or Classification in Sense 2. The work of philosophers and of taxonomists in the field of classification is generally restricted to Classification in Sense 2. (See Chap CL). 3. Classification in sense 2 plus Representing each entity by an ordinal number taken out of a system of ordinal numbers, designed to mechanise the maintenance of the sequence, 1. Either when an entity has to be replaced after having been taken out of its position; 2. Or when a new entity has to be interpolated or extrapolated in the correct place in the sequence. This ordinal number is the Class Number. (See Chap CG and CM). Classification in Sense 3 is usually practiced by large business concerns having to handle a large number of commodities. The Customs Authorities to use Classification in Sense 3 in their published list of commodities liable to customs duty. 4. Classification in Sense 3 when complete assortment is made of an amplified universe - that is, when the entities and the pseudo-entities arising in the process of successive assortment stand arranged in one filiatory sequence, each with its Class Number. (See ChapCHandCK). Classification in Sense 4 is not used very much. It is only classification in Sense 3 and Sense 5 that are frequently in demand. 5. Classification in Sense 4 with all the entities removed but only the pseudo-entities or classes retained - each class having the number representing it. (See Chap CM). It is classification in Sense 5 that is used, 1. Either when the universe classified is infinite; 2. Or when some of the entities are unknown and unknowable at any moment, even though the universe classified is finite. In particular, it is Classification in Sense 5 that is practiced by the library profession. It should be recalled that that in classification in Sense 5 1. The individual entities do not figure in the complete assortment; 2. Classes take the place of entities; and thus, 3. Each class including the Original Universe is a Class of Classes. Classification in Sense 2 has only a Scheme for Classes associated with it. But Classification in Sense 5 has a Scheme for Classification associated with it. We shall restrict the meaning of the term 'Classification' to Classification in Sense 5" (italics in original).
19- Bonifatii Mikhailovich Kedrow (1975, 1:3 emphasis original)
"Klassifikation. Verfahren zur Unterteilung eine Klasse K von Dingen usw. in Teilklassen" (628). "Die dialektisch-materialistische Einstellung zur Klassifikation besteht also nicht etwa darin, dass sie im Gegensatz zur antidialektischen die Berechtigung und den Wert von Klassifikationen bestritte, sondern darin, dass sie die These von der zeitlichen und strukturellen Relativität der Klassifikationen vertritt, während die antidialektische Auffassung die Klassifikationen in jeder Hinsicht als absolut betrachtet." This can perhaps be generalized in this way: Classification of objects means the display of connections between the objects in a certain order or in a system reflecting certain basic principles. Kedrow found that the principle of historicism must govern all natural classifications (see section 4.2cγ Genetic/historicist approaches to classification).
20- Phillip R. Sloan (1981, p. 68)
"The arrangement of objects or entities into groups or classes, usually on the basis of perceived similarity and difference."
21- ISO 5127-6 (1988, p. 93)
A classification system is an "indexing language intended for a structured representation of documents or data, through the use of indexes and corresponding terms, in order to allow systematic access, resorting to an alphabetical index, if necessary" (here cited from Simões et al. 2016, 531; note that this standard has been revised by ISO 5127:2001).
22- Lois Mai Chan (1994, p. 259)
Classification is "the multistage process of deciding on a property or characteristic of interest, distinguishing things or objects that possesses that property from those which lack it, and grouping things or objects that have the property or characteristic in common into a class. Other essential aspects of classification are establishing relationships among classes and making distinctions within classes to arrive at subclasses and finer divisions."
23- Francis L. Miksa (1994, p. 144)
"[Bibliographic] Classification is the activity of creating categories into which bibliographic items of all kinds may be placed (i.e., the work of the classificationist) and also the activity of identifying bibliographical items in terms of the categories already extant in a given system (i.e., the work of the classifier). It encompasses systems for arranging items on the shelves of libraries (sometimes called 'bibliothecal' classification), as well as systems for arranging the surrogates of items in catalogs (sometimes called 'bibliographical' classification). It includes classificatory systems based on all kinds of item characteristics (subject, form, author, citation, size, etc.), in all forms of order (logical and systematic, alphabetical, faceted, etc.), with all kinds of operating methods (pre- and post-coordinated, statistically based clustering and identification, etc.), and differing in scope from the universal to the very narrow. Finally, library classification embraces a wide range of purposes, although most often its chief purpose has been to facilitate document retrieval."
24- Frederick Wilfrid Lancaster (1998, p. 17)
Classification is "sorting items into 'conceptual classes'" and "forming classes of objects on the basis of their subject matter".
25- Geoffrey Bowker and Susan Leigh Star (1999, p. 10)
"A classification is a spatial, temporal, or spatio-temporal segmentation of the world. A 'classification system' is a set of boxes (metaphorical or literal) into which things can be placed to perform some kind of work - bureaucratic or knowledge production."
26- Arlene G. Taylor (1999, p. 237)
"The placing of subjects into categories; in organizing of information, classification is the process of determining where an information package fits into a given hierarchy and then assigning the notation associated with the appropriate level of the hierarchy to the information package and its surrogate."
27- Satija (2000, p. 222)
"Classification means to divide objects/entities (both abstract and concrete) on the basis of their differences or, conversely, the grouping of entities on the basis of their similarities. Classification is any process of dividing, sorting, grouping, arranging, ordering, ranking, mapping and correlating."
28- Elaine Svenonius (2000, p. 10)
"Organization can take many forms. Its prototypical form is classification. Classification brings like things together. In traditional classifications, like things are brought together with respect to one or more specified attributes. Any number of attributes can be used to form classes of documents embodying information, such as same size or color, same subject, or same author. However, the most important attribute for a system whose objectives is to organize information is the attribute of 'embodying the same work'. "
29- Hubert Feger (2001, 1966)
"Classification is the assignment of objects to classes". Later on, this was expanded (Feger 2015, 805): "The fundamental goal of classification is to find structures common to a group of objects, using properties to classify the objects into subgroups based on the similarity of their properties"
30- The Portuguese Language Dictionary of the Academy of Sciences (Academia das Ciências de Lisboa 2001, 837 cited in Simões et al. 2016, 531)
Classification is the "action of distributing in classes, by categories ... according to precise criteria"
31- Ernst Mayr and Walter Joseph Bock (2002, p.191)
“The logical consequence of the definition of class is that classification must be defined as the ordering of diversity into classes of similar entities. And this has been traditionally the almost universally accepted concept of classification.… A classification of organisms is based on the shared possession of their diverse attributes. The units of similarity in a Darwinian classification are called taxonomic characters that have the property of being homologous to one another in the several entities or groups. The claim of a few modern authors that there is no agreement on the definition of the word “classification” is quite misleading. Actually, prior to 1950 there was virtually total unanimity on the usage (in classification) of the words classification and class, as referring to the grouping of similar items. A classification is defined as "The arrangement of entities in a hierarchical series of nested classes, in which similar or related classes at one hierarchical level are combined comprehensively into more inclusive classes at the next higher level" (176). "Class - (in classification) A group or collection of entities (individuals), possessing attributes or traits in common ('being similar'), a kind or sort, grouped together under a general or class name. Classification - The arrangement of similar entities (objects) in a hierarchical series of nested classes, in which each more inclusive higher-level class is subdivided comprehensively into less inclusive classes at the next lower level. Darwinian classification - The ordered grouping of organisms into classes, according to their similarities and consistent with their inferred evolutionary history. Downward classification - Establishing groups by logical division. Evolutionary classification - A classification that duly considers both evolutionary processes, the ecological adaptiveness of evolutionary divergence (degree of difference) and the genealogy (phylogeny) of the taxa. Basically equal to a Darwinian classification. Hierarchical classification - The system of ranks that indicates the categorical level (level of difference) of each taxon" (191).
32- Kjeld Schmidt and Ina Wagner (2004, p. 392)
"Classification, in turn, is a special practice of categorization, involving pre-established and systematic systems of signs. That is, classification is a linguistic operation of applying a classification scheme, i.e., an ordered set of signs that is pre-established according to (a) some general principles and criteria of ordering and (b) some procedures of identification and naming. In short, an act of classification is an application of a classification scheme. Classification systems (such as thesauri) can thus be seen as instantiations of classification schemes. [...] Classifications and categorizations are both convention-based practices and equally so. But classifications are convention-based in a quite specific sense. In the case of categorization there are no pre-established principles and criteria for determining the correctness of an act of categorization. With acts of classification, however, such pre-established principles and criteria exist, in that they specify relationships between items in terms of, for example, class/ membership, part/whole, composition, cause/effect, origin/fate, function, ownership, value/risk, location, or state. Accordingly, an actor applying a classification scheme in a particular case can be held accountable in terms of the principles, criteria, and procedures of the classification scheme."
33- Dagobert Soergel (2004, p.358)
"A classification is a structure that organizes concepts into a meaningful hierarchy, possibly in a scheme of facets. The classification of living things is a taxonomy. (The term taxonomy is increasingly used for any type of classification.) A classification is now often called an ontology, particularly if it gives richer concept relationships" (bold in original omitted here).
34- Faria and Pericão (2008, p.258)
Classification is a "group of ordered concepts, distributed systematically in classes, forming a structure" and a "structuring of concepts into classes and subdivisions to express the existing semantic relationships between them" (here cited from Simões et al. 2016, 531).
35- Clare Beghtol (2010, p.1045)
"To classify means to put things into meaningful groups. Things can be physical objects, ideas, events, or anything else that human beings can perceive or imagine, and a meaningful group can be formed using any characteristic or combination of characteristics of the things. Groups can be considered to be permanent or they can be considered temporary responses to a need of the moment."
36- Ingetraut Dahlberg (2010, p. 2941)
"With this journal [International classification, 1974-1992, thereafter Knowledge organization], 'classification' was understood as a multi-meaning word that includes the following concepts: 1. classification in the sense of 'classification system', i.e., a system of classes arranged in hierarchical or faceted order; 2. classification in the sense of classifying, i.e., establishing a system of classes; 3, classification in the sense of classing, i.e., relating the classes of a classification system to objects or subjects of reality; and 4. classification in the sense of classification science, i.e., relating to this field of study and its activities" (list typography added).
37- Oxford English Dictionary (2010)
"classification, n. Origin: A borrowing from Latin. Etymon: Latin classificatio. Etymology: < post-classical Latin classificatio (1673 in a German source; 1767 in Linnaeus) > classical Latin classis class n. + -ficātiōn-, -ficātiō suffix. Compare German Klassifikation (1760 or earlier as †Classification), Swedish klassifikation (1740 as †classification), Danish klassifikation (1748), French classification (1780), Italian classificazione (1796). Compare slightly later classify v. The result of classifying; a systematic distribution, allocation, or arrangement of things in a number of distinct classes, according to shared characteristics or perceived or deduced affinities. Also: a system or method for classifying. 1. The action of classifying or arranging in classes, according to shared characteristics or perceived affinities; assignment to an appropriate class or classes. 2. A category to which something is assigned; a class."
38- Adriano Veloso and Wagner Meira (2011, p. 9)
"In a classification problem, there is a set of input-output pairs (also referred to as instances or examples) of the form zi = (xi; yi): Each input xi is a fixed-length record of the form ‹a1, . . ., al›; where each ai is an attribute-value. Each output yi draws its value from a discui8rete and finite set of possibilities y = {c1, . . ., cp}, and indicates the class to which zi belongs. Cases where yi =? indicate that the correct class of zi is unknown. There is a fixed but unknown conditional probability distribution P(y|x), that is, the relationship between inputs and outputs is fixed but unknown" "This formulation implies that the classification problem corresponds to the problem of function approximation."
39- Daniel Parrochia and Pierre Neuville (2013, p.21)
"Definition 1.9.1 We call 'classification' the operation consisting of sharing, distributing or allocating objects in classes or groups which are, in general, less numerous than them. [10] This is also the result of this operation. We want, as much as it is possible, this result to be constant, i.e. the classification must remain stable for a little transformation [11] of data".
40- WordNet 3.1 (2016-05-21)
“defines four senses of the noun 'classification' of which three are relevant for this entry: 1) "S: (n) categorization, categorisation, classification, compartmentalization, compartmentalisation, assortment (the act of distributing things into classes or categories of the same type) 2) S: (n) classification, categorization, categorisation (a group of people or things arranged by class or category) 3) (n) classification, categorization, categorisation, sorting (the basic cognitive process of arranging into classes or categories)".
Fonte: HJØRLAND, 2017, p. 122