Classification (cognitive process)

Categorization is the process in which ideas and objects are recognised, differentiated and understood. Categorization implies that objects are grouped into categories, usually for some specific purpose. Ideally, a category illuminates a relationship between the subjects and objects of knowledge. Categorization is fundamental in decision making and in all kinds of interaction with the environment. There are, however, different ways of approaching categorization.

The Classical View
The classical Aristotelian view claims that categories are discrete entities characterized by a set of properties which are shared by their members. These 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.

Cognitive science: 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 categorisation 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 categorisation at the embodied level, with similarities leading to formulation of "higher" categories, and differences leading to differentiation within categories.