 The classical theory has come under considerable pressure in the last forty years or so, not just in philosophy but in psychology and other fields as well. For psychologists, the main problem has been that the classical theory has difficulty explaining a robust set of empirical findings. At the center of this work is the discovery that certain categories are taken to be more representative or typical and that typicality scores correlate with a wide variety of psychological data (for reviews, see Smith &amp; Medin 1981, Murphy 2002). For instance, apples are judged to be more typical than plums with respect to the category of fruit, and correspondingly apples are judged to have more features in common with fruit. There are many other findings of this kind. One other is that more typical items are categorized more efficiently. For example, subjects are quicker to judge that apples are a kind of fruit than to judge that plums are. The problem isn’t that the classical theory is inconsistent with results like these but that it does nothing to explain them.