6.2. The What and Why of Categories
Categories are equivalence classes, sets or groups of things or abstract entities that we treat the same. This does not mean that every instance of a category is identical, only that from some perspective, or for some purpose, we are treating them as equivalent based on what they have in common. When we consider something as a member of a category, we are making choices about which of its properties or roles we are focusing on and which ones we are ignoring. We do this automatically and unconsciously most of the time, but we can also do it in an explicit and self-aware way.329[Cog]
[329][Cog] Cognitive science mostly focuses on the automatic and unconscious mechanisms for creating and using categories. This disciplinary perspective emphasizes the activation of category knowledge for the purpose of making inferences and “going beyond the information given,” to use Bruner’s classic phrase (Bruner 1957). In contrast, the discipline of organizing focuses on the explicit and self-aware mechanisms for creating and using categories because by definition, organizing systems serve intentional and often highly explicit purposes. Organizing systems facilitate inferences about the resources they contain, but the more constrained purposes for which resources are described and arranged makes inference a secondary goal.
Cognitive science is also highly focused on understanding and creating computational models of the mechanisms for creating and using categories. These models blend data-driven or bottom-up processing with knowledge-driven or top-down processing to simulate the time course and results of categorization at both fine-grained scales (as in word or object recognition) and over developmental time frames (as in how children learn categories). The discipline of organizing can learn from these models about the types of properties and principles that organizing systems use, but these computational models are not a primary concern to us in this book.
When we encounter objects or situations, recognizing them as members of a category helps us know how to interact with them. For example, when we enter an unfamiliar building we might need to open or pass through an entryway that we recognize as a door. We might never have seen that particular door before, but it has properties and affordances that we know that all doors have; it has a doorknob or a handle; it allows access to a larger space; it opens and closes. By mentally assigning this particular door to the “doors” category we distinguish it from “windows,” a category that also contains objects that sometimes have handles and that open and close, but which we do not normally pass through to enter another space. Categorization judgments are therefore not just about what is included in a class, but also about what is excluded from a class. Nevertheless, the category boundaries are not sharp; a “Dutch door” is divided horizontally in half so that the bottom can be closed like a door while the top can stay open like a window.
Categories are cognitive and linguistic models for applying prior knowledge; creating and using categories are essential human activities. Categories enable us to relate things to each other in terms of similarity and dissimilarity and are involved whenever we perceive, communicate, analyze, predict, or classify. Without categories, we would perceive the world as an unorganized blur of things with no understandable or memorable relation to each other. Every wall-entry we encounter would be new to us, and we would have to discover its properties and supported interactions as though we had never before encountered a door. Of course, we still often need to identify something as a particular instance, but categories enable us to understand how it is equivalent to other instances. We can interchangeably relate to something as specific as “the wooden door to the main conference room” or more generally as “any door.”
All human languages and cultures divide up the world into categories. How and why this takes place has long been debated by philosophers, psychologists and anthropologists. One explanation for this differentiation is that people recognize structure in the world, and then create categories of things that “go together” or are somehow similar. An alternative view says that human minds make sense of the world by imposing structure on it, and that what goes together or seems similar is the outcome rather than a cause of categorization. Bulmer framed the contrast in a memorable way by asking which came first, the chicken (the objective facts of nature) or the egghead (the role of the human intellect).330[Cog]
[330][Cog] However, even the way this debate has been framed is a bit controversial. Bulmer’s chicken, the “categories are in the world” position, has been described as empirical, environment-driven, bottom-up, or objectivist, and these are not synonymous. Likewise, the “egghead” position that “categories are in the mind” has been called rational, constructive, top-down, experiential, and embodied—and they are also not synonyms. See (Bulmer 1970). See also (Lakoff 1990), (Malt 1995).
A secondary and more specialized debate going on for the last few decades among linguists, cognitive scientists, and computer scientists concerns the extent to which the cognitive mechanisms involved in category formation are specialized for that purpose rather than more general learning processes.331[Cog]
[331][Cog] Is there a “universal grammar” or a “language faculty” that imposes strong constraints on human language and cognition? (Chomsky 1965) and (Jackendoff 1996) think so. Such proposals imply cognitive representations in which categories are explicit structures in memory with associated instances and properties. In contrast, generalized learning theories model category formation as the adjustment of the patterns and weighting of connections in neural processing networks that are not specialized for language in any way. Computational simulations of semantic networks can reproduce the experimental and behavioral results about language acquisition and semantic judgments that have been used as evidence for explicit category representations without needing anything like them. (Rogers and McClelland 2008) thoroughly review the explicit category models and then show how relatively simple learning models can do without them.
Even before they can talk, children behave in ways that suggest they have formed categories based on shape, color, and other properties they can directly perceive in physical objects.332[Cog] People almost effortlessly learn tens of thousands of categories embodied in the culture and language in which they grow up. People also rely on their own experiences, preferences, and goals to adapt these cultural categories or create entirely individual ones that they use to organize resources that they personally arrange. Later on, through situational training and formal education, people learn to apply systematic and logical thinking processes so that they can create and understand categories in engineering, logistics, transport, science, law, business, and other institutional contexts.
[332][Cog] The debates about human category formation also extend to issues of how children learn categories and categorization methods. Most psychologists argue that category learning starts with general learning mechanisms that are very perceptually based, but they do not agree whether to characterize these changes as “stages” or as phases in a more complex dynamical system. Over time more specific learning techniques evolve that focus on correlations among perceptual properties (things with wings tend to have feathers), correlations among properties and roles (things with eyes tend to eat), and ultimately correlations among roles (things that eat tend to sleep). See (Smith and Thelen 2003).
These three contexts of cultural, individual, and institutional categorization share some core ideas but they emphasize different processes and purposes for creating categories, so they are a useful distinction.333[Cog] Cultural categorization can be understood as a natural human cognitive ability that serves as a foundation for both informal and formal organizing systems. Individual categorization tends to grow spontaneously out of our personal activities. Institutional categorization responds to the need for formal coordination and cooperation within and between companies, governments, and other goal-oriented enterprises.
[333][Cog] These three contexts were proposed by (Glushko, Maglio, Matlock, and Barsalou 2008), who pointed out that cognitive science has focused on cultural categorization and largely ignored individual and institutional contexts. They argue that taking a broader view of categorization highlights dimensions on which it varies that are not apparent when only cultural categories are considered. For example, institutional categories are usually designed and maintained using prescriptive methods that have no analogues with cultural categories.
6.2.1. Cultural Categories
Cultural categories are the archetypical form of categories upon which individual and institutional categories are usually based. Cultural categories tend to describe our everyday experiences of the world and our accumulated cultural knowledge. Such categories describe objects, events, settings, internal experiences, physical orientation, relationships between entities, and many other aspects of human experience. Cultural categories are acquired primarily, with little explicit instruction, through normal exposure of children with their caregivers; they are associated with language acquisition and language use within particular cultural contexts.
Two thousand years ago Plato wrote that living species could be identified by “carving nature at its joints,” the natural boundaries or discontinuities between types of things where the differences are the largest or most salient. Plato’s metaphor is intuitively appealing because we can easily come up with examples of perceptible properties or behaviors of physical things that go together that make some ways of categorizing them seem more natural than others.334[Phil]
[334][Phil] This quote comes from Plato’s Phaedrus dialogue, written around 370 BCE. Contemporary philosophers and cognitive scientists commonly invoke it in discussions about whether “natural kinds” exist. . For example, see (Campbell, O’Rourke, and Slater 2011), and (Hutchins 2010), (Atran 1987), and others have argued that the existence of perceptual discontinuities is not sufficient to account for category formation. Instead, people assume that members of a biological category must have an essence of co-occurring properties and these guide people to focus on the salient differences, thereby creating categories. Property clusters enable inferences about causality, which then builds a framework on which additional categories can be created and refined. For example, if “having wings” and “flying” are co-occurring properties that suggest a “bird” category, wings are then inferred as the causal basis of flying, and wings become more salient.
Natural languages rely heavily on nouns to talk about categories of things because it is useful to have a shorthand way of referring to a set of properties that co-occur in predictable ways.335[Ling] For example, in English (borrowed from Portuguese) we have a word for “banana” because a particular curved shape, greenish-yellow or yellow color, and a convenient size tend to co-occur in a familiar edible object, so it became useful to give it a name. The word “banana” brings together this configuration of highly interrelated perceptions into a unified concept so we do not have to refer to bananas by listing their properties.336[Cog]
[335][Ling] Pronouns, adjectives, verbs, adverbs, prepositions, conjunctions, particles, and numerals and other “parts of speech” are also grammatical categories, but nouns carry most of the semantic weight.
[336][Cog] In contrast, the set of possible interactions with even a simple object like a banana is very large. We can pick, peel, slice, smash, eat, or throw a banana, so instead of capturing this complexity in the meaning of banana it gets parceled into the verbs that can act on the banana noun. Doing so requires languages to use verbs to capture a broader and more abstract type of meaning that is determined by the nouns with which they are combined. Familiar verbs like “set,” “put,” and “get” have dozens of different senses as a result because they go with so many different nouns. We set fires and we set tables, but fires and tables have little in common. The intangible character of verbs and the complexity of multiple meanings make it easier to focus instead on their associated nouns, which are often physical resources, and create organizing systems that emphasize the latter rather than the former. We create organizing systems that focus on verbs when we are categorizing actions, behaviors, or services where the resources that are involved are less visible or less directly involved in the supported interactions.
Languages differ a great deal in the words they contain and also in more fundamental ways that they require speakers or writers to attend to details about the world or aspects of experience that another language allows them to ignore. This idea is often described as linguistic relativity. (See the sidebar, Linguistic Relativity.)
For example, speakers of the Australian aboriginal language, Guugu Yimithirr, do not use concepts of left and right, but rather use compass-point directions. Where in English we might say to a person facing north, “Take a step to your left,” they would use their term for west. If the person faced south, we would change our instruction to “right,” but they would still use their term for west. Imagine how difficult it would be for a speaker of Guugu Yimithirr and a speaker of English to collaborate in organizing a storage room or a closet.338[Cog]
[338][Cog] This analysis comes from (Haviland 1998). More recently, Lera Boroditsky has done many interesting studies and experiments about linguistic relativity. See (Boroditksy 2003) for an academic summary and (Boroditsky 2010, 2011) for more popular treatments.
It is not controversial to notice that different cultures and language communities have different experiences and activities that give them contrasting knowledge about particular domains. No one would doubt that university undergraduates in Chicago would think differently about animals than inhabitants of Guatemalan rain forests, or even that different types of “tree experts” (taxonomists, landscape workers, foresters, and tree maintenance personnel) would categorize trees differently.339[Cog]
On the other hand, despite the wide variation in the climates, environments, and cultures that produce them, at a high level “folk taxonomies” that describe natural phenomena are surprisingly consistent around the world. Half a century ago the sociologists Emile Durkheim and Marcel Mauss observed that the language and structure of folk taxonomies mirrors that of human family relationships (e.g., different types of trees might be “siblings,” but animals would be part of another family entirely). They suggested that framing the world in terms of familiar human relationships allowed people to understand it more easily; this was ultimately reflected in complex mythological systems, such as Greek mythology, where genealogical relationships between gods represented category relationships among the phenomena with which they were associated. As human knowledge grew and the taxonomies became more comprehensive and complex, Durkheim and Mauss argued, they lay the groundwork for scientific classifications and shed their mythological roots.339a[Cog]
Anthropologist Brent Berlin, a more recent researcher, concurs with Durkheim and Mauss’s observation that kinship relations and folk taxonomies are related, but argues that humans patterned their family structures after the natural world, not the other way around. Berlin also observed that folk taxonomies invariably classify natural phenomena into a five- or six-level hierarchy, with one of the levels being the psychologically primary or “real” name (such as “cat” or “dog”), as opposed to more abstract names (e.g. “mammal”) that are used less in everyday life. Organizing system designers should account for this tendency when creating systems for human users: classifications with many more levels may be too deep or difficult for users to navigate effectively.339b[Cog]
6.2.2. Individual Categories
Individual categories are created in an organizing system to satisfy the ad hoc requirements that arise from a person’s unique experiences, preferences, and resource collections. Unlike cultural categories, which usually develop slowly and last a long time, individual categories are created by intentional activity, in response to a specific situation, or to solve an emerging organizational challenge. As a consequence, the categories in individual organizing systems generally have short lifetimes and rarely outlive the person who created them.340[Arc]
[340][Arc] The personal archives of people who turn out to be famous or important are the exception that proves this rule. In that case, the individual’s organizing system and its categories are preserved along with their contents.
Individual categories draw from cultural categories but differ in two important ways. First, individual categories sometimes have an imaginative or metaphorical basis that is meaningful to the person who created them but which might distort or misinterpret cultural categories. Second, individual categories are often specialized or synthesized versions of cultural categories that capture particular experiences or personal history. For example, a person who has lived in China and Mexico, or lived with people from those places, might have highly individualized categories for foods they like and dislike that incorporate characteristics of both Chinese and Mexican cuisine.
Individual categories in organizing systems also reflect the idiosyncratic set of household goods, music, books, website bookmarks, or other resources that a person might have collected over time. The organizing systems for financial records, personal papers, or email messages often use highly specialized categories that are shaped by specific tasks to be performed, relationships with other people, events of personal history, and other highly individualized considerations.
Traditionally, individual categorization systems were usually not visible to, or shared with, others, whereas, this has become an increasingly common situation for people using web-based organizing system for pictures, music, or other personal resources. On websites like the popular Flickr site for photos, people typically use existing cultural categories to tag their photos as well as individual ones that they invent. In particular, the typical syntactic constraint that tags are delimited by white space encourages the creation of new categories by combining existing category names using concatenation and camel case conventions; photos that could be categorized as “Berkeley” and “Student” are thus tagged as “BerkeleyStudent.” Similar generative processes for creating individual category names are used with Twitter “hashtags” where tweets about events are often categorized with an ad hoc tag that combines an event name and a year identifier like “#NBAFinals15.” Web-based documents and product pages in web catalogs are commonly categorized with “ReadThis” and “BuyThis” tags that are meaningful for the individuals who created those categories for themselves, but which are not very informative for anyone else.
6.2.3. Institutional Categories
In contrast to cultural categories that are created and used implicitly, and to individual categories that are used by people acting alone, institutional categories are created and used explicitly and rationally, and most often by many people or computational agents in coordination with each other. Institutional categories are most often created in abstract and information-intensive domains where unambiguous and precise categories are needed to regulate and systematize activity, to enable information sharing and reuse, and to reduce transaction costs. Furthermore, instead of describing the world as it is, institutional categories are usually defined to change or control the world by imposing semantic models that are more formal and arbitrary than those in cultural categories. Laws, regulations, and standards often specify institutional categories, along with decision rules for assigning resources to new categories, and behavior rules that prescribe how people must interact with them. The rigorous definition of institutional categories enables classification: the systematic assignment of resources to categories in an organizing system.341[Law]
[341][Law] Consider how the cultural category of “killing a person” is refined by the legal system to distinguish manslaughter and different degrees of murder based on the amount of intentionality and planning involved (e.g., first and second degree murder) and the roles of people involved with the killing (accessory). In general, the purpose of laws is to replace coarse judgments of categorization based on overall similarity of facts with rule-based categorization based on specific dimensions or properties.
Creating institutional categories by more systematic processes than cultural or individual categories does not prevent them from being biased. Indeed, the goal of institutional categories is often to impose or incentivize biases in interpretation or behavior. There is no better example of this than the practice of gerrymandering, designing the boundaries of election districts to give one political party or ethnic group an advantage. The word was invented in 1812 in a newspaper article critical of Massachusetts governor Elbridge Gerry, who oversaw the creation of biased electoral districts. One such district was so contorted in shape, it was said to look like a salamander, and thus was called a Gerrymander. The practice remains widespread, but nowadays sophisticated computer programs can select voters on any number of characteristics and create boundaries that either “pack” them into a single district to concentrate their voting power or “crack” them into multiple districts to dilute it.
Institutional categorization stands apart from individual categorization primarily because it invariably requires significant efforts to reconcile mismatches between existing individual categories, where those categories embody useful working or contextual knowledge that is lost in the move to a formal institutional system.342[Bus]
[342][Bus] The particularities or idiosyncrasies of individual categorization systems sometimes capture user expertise and knowledge that is not represented in the institutional categories that replace them. Many of the readers of this book are information professionals whose technological competence is central to their work and which helps them to be creative. But for a great many other people, information technology has enabled the routinization of work in offices, assembly lines, and in other jobs where new institutionalized job categories have “downskilled” or “deskilled” the nature of work, destroying competence and engendering a great deal of resistance from the affected workers.
Institutional categorization efforts must also overcome the vagueness and inconsistency of cultural categories because the former must often conform to stricter logical standards to support inference and meet legal requirements. Furthermore, institutional categorization is usually a process that must be accounted for in a budget and staffing plans. While some kinds of institutional categories can be devised or discovered by computational processes, most of them are created through the collaboration of many individuals, typically from various parts of an organization or from different firms.343[Bus]
[343][Bus] Similar technical concerns arise in within-company and multi-company
standardization efforts, but the competitive and potentially
anti-competitive character of the latter imposes greater complexity by
introducing considerations of business strategy and politics. Credible
standards-making in multi-company contexts depends on an explicit and
transparent process for gathering and prioritizing requirements, negotiating
specifications that satisfy them, and ensuring conformant
implementations—without at any point giving any
participating firm an advantage. See the
OASIS Technical
Committee Process for an example
(https://www.oasis-open.org/policies-guidelines/tc-process)
and (Rosenthal
et al. 2004) for an analysis of best practices.
The different business or technical perspectives of the participants are often the essential ingredients in developing robust categories that can meet carefully identified requirements. And as requirements change over time, institutional categories must often change as well, implying version control, compliance testing, and other formal maintenance and governance processes.
Some institutional categories that initially had narrow or focused applicability have found their way into more popular use and are now considered cultural categories. A good example is the periodic table in chemistry, which Mendeleev developed in 1869 as a new system of categories for the chemical elements. The periodic table proved essential to scientists in understanding their properties and in predicting undiscovered ones. Today the periodic table is taught in elementary schools, and many things other than elements are commonly arranged using a graphical structure that resembles the periodic table of elements in chemistry, including sci-fi films and movies, desserts, and superheroes. Unfortuntely, in this transition from science to popular culture, many of these so-called periodic tables are just ad hoc collections that ignore the essential idea that the rows and columns capture explanatory principles about resource properties that vary in a periodic manner. A notable exception is Andrew Plotkin's Periodic Table of Dessert.344[Cog]
[344][Cog] See (Suehle 2012) and Plotkin's table at (Periodic Table of Dessert).
6.2.4. A “Categorization Continuum”
As we have seen, the concepts of cultural, individual, and institutional categorization usefully distinguish the primary processes and purposes for creating categories. However, these three kinds of categories can fuse, clash, and recombine with each other. Rather than viewing them as having precise boundaries, we might view them as regions on a continuum of categorization activities and methods.
Consider a few different perspectives on categorizing animals as an example. Scientific institutions categorize animals according to explicit, principled classification systems, such as the Linnaean taxonomy that assigns animals to a phylum, class, order, family, genus and species. Cultural categorization practices cannot be adequately described in terms of a master taxonomy, and are more fluid, converging with principled taxonomies sometimes, and diverging at other times. While human beings are classified within the animal kingdom in biological classification systems, people are usually not considered animals in most cultural contexts. Sometimes a scientific designation for human beings, homo sapiens is even applied to human beings in cultural contexts, since the genus-species taxonomic designation has influenced cultural conceptions of people and (other) animals over the years.
Animals are also often culturally categorized as pets or non-pets. The category “pets” commonly includes dogs, cats, and fish. A pet cat might be categorized at multiple levels that incorporate individual, cultural, and institutional perspectives on categorization—as an “animal” (cultural/institutional), as a “mammal” (institutional), as a “domestic short-hair” (institutional) as a “cat” (cultural), and as a “troublemaker” or a “favorite” (individual), among other possibilities, in addition to being identified individually by one or more pet names. Furthermore, not everyone experiences pets as just dogs, cats and fish. Some people have relatively unusual pets, like pigs. For individuals who have pet pigs or who know people with pet pigs, “pigs” may be included in the “pets” category. If enough people have pet pigs, eventually “pigs” could be included in mainstream culture’s pet category.
Categorization skewed toward cultural perspectives incorporate relatively traditional categories, such as those learned implicitly from social interactions, like mainstream understandings of what kinds of animals are “pets,” while categorization skewed toward institutional perspectives emphasizes explicit, formal categories, like the categories employed in biological classification systems.