1. Classifying things: dividing them into groups according to shared characteristics and labelling these. Taxonomy is the name given to the activity of systematic categorization (e.g. taxonomies of genre and of communicative functions). Categorization differs between languages (see also Sapir-Whorf hypothesis). In the representation of people, categorization generates stereotypes.
2. In perception, the automatic and unconscious mental process of classifying sensory data. See also schemata.
3. (philosophy) Seeking fundamental divisions of reality into types (see also ontology). Aristotle divided reality into ten categories: substance, quantity, quality, relation, action, affection, place, time, position, and state. Kant arrived at four: quantity, quality, relation, and modality. Peirce used three as the basis of his semiotics: firstness (undifferentiated quality), secondness (blind force), and thirdness (mediation).