What does it mean that prototype-based categories?

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.

Try this: Pick a category you use frequently — 'productive day,' 'good meeting,' 'useful tool,' or 'interesting person.' Write down the prototype: what does the most typical example look like? Then list three items that belong to the category but feel less typical. Arrange them from most to least prototypical. You've just made your implicit typicality gradient explicit — and you can now ask whether that gradient is serving you or distorting your judgment.