Categorization

Categorization is the process in which experiences and concepts are recognised and understood. Categorization implies that concepts are classified into categories based on commonalities and usually for some specific purpose. Categorization is fundamental in decision making, in all kinds of interaction with the environment, and in language. Categorization is central issue in Cognitive Linguistics in which it is argued to be one of the primary principles of conceptual and linguistic organization. However, categorization in Cognitive Linguistics differs radically from the classical Aristotelian model.

The Aristotelian category
The classical Aristotelian view claims that categories are discrete entities characterized by a set of property properties which are shared by all of their members. These properties are assumed to establish the conditions which are both necessary and sufficient to capture meaning.

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

Prototype categories
In the wake of the Cognitive Revolution of the 1970s, studies by cognitive scientists like Eleanor Rosch, Brent Berlin, Paul Kay, and George Lakoff, indicated that there were several problems with the classical view:


 * Necessary conditions are inadequate: the idea of necessary and sufficient conditions is rarely if ever met in categories of naturally occurring things or in humans' categorization of experiences
 * There are degrees of membership: humans tend to regard some members of categories as better members than others
 * Boundaries between categories are not clear cut: natural categories tend to be fuzzy at their boundaries and inconsistent in the status of their constituent members

With these observations in mind, cognitive scientists argue that categorization the process of grouping things based on prototypes. It has also been suggested that categorisation based on prototypes is the basis for human development, and that this learning relies on learning about the world via embodiment. Systems of categories are not objectively "out there" in the world but are rooted in people's experience.

The structure of categories
Categories form part of a hierarchical taxonomic structure organized in accordance with at least three structural principles: radial structure, inheritance, and levels of categorization.

Radial structure
The notion of radial structure with introduced by Lakoff (1987), and implies that categories do not have symmetric structures. A radial structure is a taxonomy that has a center-periphery structure, such that the center of the category provides the schema of prototypical properties. The center is itself an idealization over what the membres of the category have, or should have, in common.

The more in common a member has with the prototypical center, the closer to the center it is located. That is, those members that do not share a lot of features with the center are peripherally located. Thus categories display graded centrality and degree of membership, with good members towards the center and bad members towards the boundary.

Inheritance
Members of categories, which are also called instances of categories, are said to inherit properties from the schema - the more they inherit, the better members, they are. However, sometimes members of a category are categories themselves, in which case they are called subsets or subcategories. Subcategories are considered extensions of the schema, because they provide a sets of properties themselves, only some of which are inherited from the schema.

Levels of categorization
Taxonimies of categories are organized into levels of categorization. There are three levels:


 * Superordinate level: Superordinate categories are the most general ones. They are the ones that are at the top of a folk taxonomy).
 * Basic, or generic, level: categories at the basic, or middle, level are perceptually and conceptually the more salient. The generic level of a category tends to elicit the most responses and richest images, providing a basic gestalt, and seems to be the psychologically basic level. Basic level categories are members of superordinate level categories.
 * Subordinate level: Subordinate level categories are the most specific ones. They are the members of the basic level categories. They have clearly identifiable gestalts and many individuating specific features.