When people categorize objects they rarely check a strict list of necessary features. Instead they compare the new item to a mental prototype—the best or most typical example of the category. A robin is a better bird prototype than a penguin. A desk chair is a better furniture prototype than a beanbag.

Prototype theory, developed by Eleanor Rosch, treats categories as organized around central tendencies. Membership is graded. Some members are clearer than others. Features that appear frequently across category members become more diagnostic. The approach explains why people respond faster and more confidently to typical instances.

Prototypes are not fixed photographs. They can be abstract averages formed from experience. Cultural and individual differences shape what counts as typical. Still, the core claim remains that natural categories are structured around resemblance to an ideal rather than by classical definitions.

• Best or most typical category member
• Graded membership rather than all-or-none
• Based on family resemblance
• Explains typicality effects in reaction time

The theory has influenced research on concepts, language, and even clinical diagnosis of mental disorders.