Prototype Theory

Cognitive scientific theory that suggests we categorize things and ideas according to a "family resemblance" rather than by requiring something have all necessary and sufficient conditions.

For example, you might think of a chair in your mind is defined by having four legs, a seat, and a backrest, but when you encounter an office chair or a stool with a backrest, the category divisions get fuzzy. Rather than throwing out the office chair, you accept it as a chair, even though it has a wheeled base instead of four legs. Maybe you decide the stool with the backrest is just a tall chair, or maybe it's a weird stool.