Categorization is an activity that consists of putting things (objects, ideas, people) into categories (classes, types, index) based on their similarities or common criteria. It allows humans to organize things, objects, and ideas that exist around them and simplify their understanding of the world.[1] Categorization is something that humans and other organisms do: "doing the right thing with the right kind of thing." The activity of categorizing things can be nonverbal or verbal. For humans, both concrete objects and abstract ideas are recognized, differentiated, and understood through categorization. Objects are usually categorized for some adaptive or pragmatic purposes.

Categorization is grounded in the features that distinguish the category's members from nonmembers. Categorization is important in learning, prediction, inference, decision making, language, and many forms of organisms' interaction with their environments.

There are many theories of categorization, among them:

  • Classical categorization
  • Conceptual clustering
  • Prototype theory

Theories about categorization

The classical view on categorization

Classical categorization first appears in the context of Western Philosophy in the work of Plato, who, in his Statesman dialogue, introduces the approach of grouping objects based on their similar properties. This approach was further explored and systematized by Aristotle in his Categories treatise, where he analyzes the differences between classes and objects. Aristotle also applied intensively the classical categorization scheme in his approach to the classification of living beings (which uses the technique of applying successive narrowing questions such as "Is it an animal or vegetable?", "How many feet does it have?", "Does it have fur or feathers?", "Can it fly?"...), establishing this way the basis for natural taxonomy.

According to the classical Aristotelian view, categories are discrete entities characterized by a set of features that are shared by their members. In analytic philosophy, these features are assumed to establish the conditions which are both necessary and sufficient conditions to capture meaning.

In the classical view, categories need to be clearly defined, mutually exclusive and collectively exhaustive. This way, any entity in the given classification universe belongs unequivocally to one, and only one, of the proposed categories.

Modern versions of classical categorization theory study how the brain learns and represents categories by detecting the features that distinguish members from nonmembers.[2][3]

Conceptual clustering

Conceptual clustering is a modern variation of the classical approach of categorization, and derives from attempts to explain how knowledge is represented. In this approach, classes (clusters or entities) are generated by first formulating their conceptual descriptions and then classifying the entities according to the descriptions.[4]

Conceptual clustering developed mainly during the 1980s, as a machine paradigm for unsupervised learning. It is distinguished from ordinary data clustering by generating a concept description for each generated category.

Categorization tasks in which category labels are provided to the learner for certain objects are referred to as supervised classification, supervised learning, or concept learning. Categorization tasks in which no labels are supplied are referred to as unsupervised classification, unsupervised learning, or data clustering. The task of supervised classification involves extracting information from the labeled examples that allows accurate prediction of class labels of future examples. This may involve the abstraction of a rule or concept relating observed object features to category labels, or it may not involve abstraction (e.g., exemplar models). The task of clustering involves recognizing inherent structure in a data set and grouping objects together by similarity into classes. It is thus a process of generating a classification structure.

Conceptual clustering is closely related to fuzzy set theory, in which objects may belong to one or more groups, in varying degrees of fitness.

Prototype theory

Since the research by Eleanor Rosch and George Lakoff in the 1970s, categorization can also be viewed as the process of grouping things based on prototypes—the idea of necessary and sufficient conditions is almost never met in categories of naturally occurring things. It has also been suggested that categorization based on prototypes is the basis for human development, and that this learning relies on learning about the world via embodiment.

A cognitive approach accepts that natural categories are graded (they tend to be fuzzy at their boundaries) and inconsistent in the status of their constituent members.

Systems of categories are not objectively "out there" in the world but are rooted in people's experience. Conceptual categories are not identical for different cultures, or indeed, for every individual in the same culture.

Categories form part of a hierarchical structure when applied to such subjects as taxonomy in biological classification: higher level: life-form level, middle level: generic or genus level, and lower level: the species level. These can be distinguished by certain traits that put an item in its distinctive category. But even these can be arbitrary and are subject to revision.

Categories at the middle level are perceptually and conceptually the more salient. The generic level of a category tends to elicit the most responses and richest images and seems to be the psychologically basic level. Typical taxonomies in zoology for example exhibit categorization at the embodied level, with similarities leading to formulation of "higher" categories, and differences leading to differentiation within categories.

Social categorization

Social categorization consists of putting human beings into groups in order to identify them based on different criteria. Categorization is a process studied by scholars in cognitive science but can also be studied as a social activity. Social categorization is different from the categorization of other things because it implies that people create categories for themselves and others as human beings.[1] Groups can be created based on ethnicity, country of origin, religion, sexual identity, social privileges, economic privileges, etc. Various ways to sort people exist according to one’s schemas. People belong to various social groups because of their ethnicity, religion, or age.[5]

Social categories based on age, race, and gender are used by people when they encounter a new person. Because some of these categories refer to physical traits, they are often used automatically when people don’t know each other.[6] These categories are not objective and depend on how people see the world around them. They allow people to identify themselves with similar people and to identify people who are different. They are useful in one's identity formation with the people around them. One can build their own identity by identifying themselves in a group or by rejecting another group.[7]

Social categorization is similar to other types of categorization since it aims at simplifying the understanding of people. However, creating social categories implies that people will position themselves in relation to other groups. A hierarchy in group relations can appear as a result of social categorization.[7]

Scholars argue that the categorization process starts at a young age when children start to learn about the world and the people around them. Children learn how to know people according to categories based on similarities and differences. Social categories made by adults also impact their understanding of the world. They learn about social groups by hearing generalities about these groups from their parents. They can then develop prejudices about people as a result of these generalities.[6]

Another aspect about social categorization is mentioned by Stephen Reicher and Nick Hopkins and is related to political domination. They argue that political leaders use social categories to influence political debates.[5]

Negative aspects of social categorization

The activity of sorting people according to subjective or objective criteria can be seen as a negative process because of its tendency to lead to violence from a group to another.[8] Indeed, similarities gather people who share common traits but differences between groups can lead to tensions and then the use of violence between those groups. The creation of social groups by people is responsible of a hierarchization of relations between groups.[8] These hierarchical relations participate in the promotion of stereotypes about people and groups, sometimes based on subjective criteria. Social categories can encourage people to associate stereotypes to groups of people. Associating stereotypes to a group, and to people who belong to this group, can lead to forms of discrimination towards people of this group.[9] The perception of a group and the stereotypes associated with it have an impact on social relations and activities.

Some social categories have more weight than others in society. For instance, in history and still today, the category of "race" is one of the first categories used to sort people. However, only a few categories of race are commonly used such as "Black", "White", "Asian" etc. It participates in the reduction of the multitude of ethnicities to a few categories based mostly on people's skin color.[10]

The process of sorting people creates a vision of the other as ‘different’, leading to the dehumanization of people. Scholars talk about intergroup relations with the concept of Social identity theory developed by H. Tajfel.[8] Indeed, in history, many examples of social categorization have lead to forms of domination or violence from a dominant group to a dominated group. Periods of colonisation are examples of times when people from a group chose to dominate and control other people belonging to other groups because they considered them as inferior. Racism, discriminations and violence are consequences of social categorization and can occur because of it. When people see others as different, they tend to develop hierarchical relation with other groups.[8]

See also: Social identity theory


There cannot be categorization without the possibility of miscategorization. To do "the right thing with the right kind of thing."[11], there has to be both a right and a wrong thing to do. Not only does a category of which "everything" is a member lead logically to the Russell paradox ("is it or is it not a member of itself?"), but without the possibility of error, there is no way to detect or define what distinguishes category members from nonmembers.

An example of the absence of nonmembers is the problem of the poverty of the stimulus in language learning by the child: children learning the language do not hear or make errors in the rules of Universal Grammar (UG). Hence they never get corrected for errors in UG. Yet children's speech obeys the rules of UG, and speakers can immediately detect that something is wrong if a linguist generates (deliberately) an utterance that violates UG. Hence speakers can categorize what is UG-compliant and UG-noncompliant. Linguists have concluded from this that the rules of UG must be somehow encoded innately in the human brain.[12]

Ordinary categories, however, such as "dogs," have abundant examples of nonmembers (cats, for example). So it is possible to learn, by trial and error, with error-correction, to detect and define what distinguishes dogs from non-dogs, and hence to correctly categorize them.[13] This kind of learning, called reinforcement learning in the behavioral literature and supervised learning in the computational literature, is fundamentally dependent on the possibility of error, and error-correction. Miscategorization -- examples of nonmembers of the category -- must always exist, not only to make the category learnable, but for the category to exist and be definable at all.

See also


  1. McGarty, Craig, et al. “Social Categorization.” International Encyclopedia of the Social & Behavioral Sciences, 2015, pp. 186–191.
  2. Ashby, F. G., & Valentin, V. V. (2017). Multiple systems of perceptual category learning: Theory and cognitive tests. In: Cohen, H., & Lefebvre, C. (Eds.). (2017).Handbook of Categorization in Cognitive Science (2nd edition). Elsevier.
  3. Pérez-Gay Juárez, F., Thériault, C., Gregory, M., Rivas, D., Sabri, H., & Harnad, S. (2017). How and Why Does Category Learning Cause Categorical Perception? International Journal of Comparative Psychology, 30.
  4. Kaufman K.A. (2012) Conceptual Clustering. In: Seel N.M. (eds) Encyclopedia of the Sciences of Learning. Springer, Boston, MA
  5. Reicher, S, and N Hopkins. “Psychology and the End of History: a Critique and a Proposal for the Psychology of Social Categorization.” Political Psychology, vol. 22, no. 2, 2001, pp. 383–407.
  6. Liberman, Zoe, et al. “The Origins of Social Categorization.” Trends In Cognitive Sciences, vol. 21, no. 7, 2017, pp. 556–568.
  7. Bodenhausen, Galen & Kang, S.K. & Peery, D.. (2012). Social categorization and the perception of social groups. 10.4135/9781446247631.n16.
  8. Tajfel, H. “Social Psychology of Intergroup Relations.” Annual Review of Psychology, vol. 33, no. 1, 1982, pp. 1–39.
  9. Hugenberg, Kurt, and Galen V. Bodenhausen. “Ambiguity in Social Categorization: The Role of Prejudice and Facial Affect in Race Categorization.” Psychological Science, vol. 15, no. 5, 2004, pp. 342–345.
  10. Nadine Chaurand. Stéréotypisation. Catégorisation sociale. Dictionnaire historique et critique du racisme, PUF, 10p, 2013. ffhal-00966930
  11. Cohen & Lefebvre 2017
  12. Lasnik, H., & Lidz, J. L. (2017). The Argument from the Poverty of the Stimulus. In: Ian Roberts (ed.) The Oxford Handbook of Universal Grammar.
  13. Burt, J. R., Torosdagli, N., Khosravan, N., RaviPrakash, H., Mortazi, A., Tissavirasingham, F., ... & Bagci, U. (2018). Deep learning beyond cats and dogs: recent advances in diagnosing breast cancer with deep neural networks British Journal of Radiology, 91(1089), 20170545.
  • To Cognize is to Categorize: Cognition is Categorization
  • Wikipedia Categories Visualizer
  • Interdisciplinary Introduction to Categorization: Interview with Dvora Yanov (political sciences), Amie Thomasson (philosophy) and Thomas Serre (artificial intelligence)
  • "Category" . Encyclopædia Britannica. 5 (11th ed.). 1911. pp. 508–510.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.