What is prototype theory?

Prototype theory is a concept in personal epistemology: Many real categories are organized around a central example rather than strict rules.

Example: Ask ten people to name a bird. Most will say robin or sparrow — not penguin, ostrich, or kiwi. All five are equally birds by any biological definition, yet your mind treats robin as the 'real' bird and penguin as an edge case. Your categories don't work by checking a definition. They work by comparing to a central example — a prototype — and judging similarity.

This concept is part of Phase 12 (Classification and Typing) in the How to Think curriculum, which builds the epistemic infrastructure for classification and typing.