The Discipline of Organizing: Core Concepts Edition, 3rd Edition

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.

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 ...