A taxonomy is a kind of knowledge organization system. Etymologically "taxonomy comes from Greek taxis : "arrangement, order" and nomos, "law". The units in taxonomies are termed taxon (plural: taxa). "Initially taxonomy was only the science of classifying living organisms, but later the word was applied in a wider sense, and may also refer to either a classification of things, or the principles underlying the classification." (Wikipedia, 2005).


The word taxonomy is sometimes used synonymously with classification and sometimes given a special meaning. The use of the word is partly determined by idiosyncrasies or different traditions. It is, for example, much used in biology, but not in chemistry even if The periodic system is considered a model of a taxonomy:


"Chemistry and physics provide a well-known example of a classification, which is seldom labeled a taxonomy but most certainly represents one: the Periodic Table of the Elements, in which chemical elements are arranged in a highly structured format according to inherent properties. One measure of the validity and usefulness of the Periodic Table is its power to predict new elements, a function at which it excels. Another measure of its strength is its descriptive power; the taxonomic structure of the Periodic Table represents very detailed knowledge about any given element, and the ability to read the table enables one to learn much about elements and their relationships to each other." (Grove, 2003, p. 2771).


Some attempts to differentiate taxonomies and classifications are:


“A taxonomy obtains when several fundamenta divisionis are considered in succession, rather than simultaneously, by an intensional cl. [classification]. The order in which fundamenta are considered is highly relevant: the taxonomy obtained by using property X to classify a genus and then property Y to classify its species is by no means the same as that obtained by considering property Y first and property X afterwards.” (Marradi, 1990).


"Classification versus taxonomy versus systematics?
The majority view is that "systematics" is the more general term, being defined as the study of organismal diversity, whereas "taxonomy" is more narrowly the set of procedures and rules for naming entities (taxa) and producing "classifications" (ordering and/or nesting of taxa)." (Mishler, 2006)


"Purist definition of a taxonomy –terms have parent/child relationship." (Earley, 2005).


Campbell & Currier (31/10/00) asks: What is a taxonomy? And they provide the following answer: "

Examples of taxonomies:


"A taxonomy is not simply a neutral structure for categorizing specimens. It implicitly embodies a theory of the universe from which those specimens are drawn. It defines what data are to be recorded and how like and unlike specimens are to be distinguished. In creating a taxonomy of computer program security flaws, we are in this way creating a theory of such flaws, and if we seek answers to particular questions from a collection of flaw instances, we must organize the taxonomy accordingly." Landweh et al. (1994).


“For the purposes of this chapter, we will use the term taxonomy inclusively to refer to any classified collection of elements.” Susan Conway and Char Sligar (2002) Unlocking Knowledge Assets Microsoft Press


"Any set of entities can be classified in indefinitely many ways. Books can be classified according to author, title, subject matter, and so on. Although these various classifications can be integrated into a single reference system so that any book can be retrieved on a variety of different counts, books as physical objects can be arrayed on library shelves in only one order. Even here, contingent problems arise. For example, very large books may have to be shelved out of order, and expensive first editions may be locked away in separate collections.

More stringent requirements apply to scientific classifications. The ultimate goal for scientific classifications is to group entities so that these classes function in, or facilitate the formation of, scientific laws (see Laws, natural §1). Aristotle divided motion into super- and sub-lunar as well as forced and natural (see Mechanics, Aristotelian). The primary justification of his classification was the system of laws that he was able to generate using it. When Newton introduced his quite different system, his classification replaced Aristotle’s because Newton’s system of laws was more powerful, accurate and inclusive. In general, systems of scientific classification are intimately connected to scientific theories and cannot be evaluated independently of them. Different sorts of theories require different classifications.

One major difference is between structural and historical classifications. The periodic table of physical elements is structural. The elements are individuated and ordered linearly according to their atomic number. Hydrogen comes first, then helium, lithium, and so on. These elements in turn can be arranged hierarchically as metals, rare earths, and so on. Some of these arrangements are perfectly nested; others are not. A more contemporary classification would include reference to subatomic particles and their relations (see Chemistry, philosophical aspects of §4). In general, structural hierarchies do not include very many levels. They are not very deep. Although cosmology is a legitimate area of physics, no one has suggested a historical classification of the physical elements; for example, classifying them in the order in which they appeared after the Big Bang." (
Hull, 1998).


According to Aida Slavic is there a difference between classifications and taxonomies:

"Knowledge classification can be, and often is, TAXONOMIC (sometimes called 'entity classification' [or Phenomenon classification]) like the classification of zoology, classification of plants, or classification of chemical elements (which means that they are going to list one concept in one place only in the classification structure).

    Bibliographic classifications i.e. those one has to use to describe real documents ARE NOT and CAN NOT be taxonomic. They are by all means ASPECT or disciplinary classifications. This means that they will list one concept in all disciplines and fields where that concept might be studied: e.g. 'water' will have to appear under chemistry, physics, in geology, medicine, sport etc.

    This is of critical importance for information retrieval as aspect classification helps to establish the context in which one concept or phenomenon might be studied within the document." (Slavic, 2000).


This quote by Slavic is, however, wrong: Bibliographical classifications may be phenomenon classifications (see, for example, Brown). Library classification systems like the Dewey Decimal Classification (DDC) are also sometimes termed "taxonomies" (cf., Campbell & Currier, 31/10/00). The demand that taxonomies must not be aspect or disciplinary organized is thus without support. It is correct that the origin of taxonomies are in biology and are classifications of organisms, but the term is today used much broader.  


Meehl (1995) calls for a rigorous application of specific diagnostic criteria: “I see classification as an enterprise that aims to carve nature at its joints (Plato), identifying categories of entities that are non-arbitrary, non-man made.”





Bailey, K. D. (1994). Typologies and Taxonomies: An Introduction to Classification Techniques. London: Sage Publications. (Quantitative Applications in the Social Sciences).


Campbell, L. M. & Currier, S. (31/10/00).


Earley, S. (2005). Resolving Taxonomy Challenges and Information Architecture Conflicts.


Fabian J., 1975, “Taxonomy and Ideology: On the Boundaries of Concept Classification”. IN: M. Kinkade (ed.). Linguistics and Anthropology, Lisse, pp. 183-197.


Gilchrist, A (2003). Thesauri, taxonomies and ontologies - an etymological note. Journal of Documentation, 59 (1). 7 - 18.


Grove, A. (2003). Taxonomy. In: Encyclopedia of Library and Information Science, pp. 2770-2777. New York: Marcel Dekker, Inc


Hempel, C. G. (1965). Fundamentals of Taxonomy (pp. 137-154). In C. G. Hempel: Aspects of scientific explanation and other essays in the philosophy of science. New York: The Free Press.


Hull, D. L. (1998). Taxonomy. IN: Routledge Encyclopedia of Philosophy, Version 1.0, London: Routledge.


Landwehr, C. E.; Bull, A. R.; McDermott, J. P. & Chpi, W. S. (1994). A Taxonomy of Computer Program Security Flaws, with Examples. ACM Computing Surveys, 26,3 (Sept. 1994)


Marradi, A. (1990). Classification, Typology, Taxonomy. Quality and Quantity, XXIV, 2, 129-157. Available at:

(Visited January 4, 2004)


Meehl, P. E. (1995). Bootstraps taxometrics: solving the classification problem in psychopathology. American Psychologist, 50(4), 266-275.


Mishler, B. D. (2006). Integrative Biology 200A: "Principles of phylogenetics".


Slavic, A. (2000). A Definition of Thesauri and Classification as Indexing Tools

(Visited 20-12-2005).


Welty, C. A. (1998). The Ontological Nature of Subject Taxonomies. IN: N. Guarino (ed.), Proceedings of the First Conference on Formal Ontology and Information Systems, Amsterdam, IOS Press.



Wikipedia. The free encyclopedia. (2005). Taxonomy.



See also: Knowledge organization systems



Birger Hjørland

Last updated: 02-08-2007