What are categories and concepts?

This chapter considers more carefully the question of just what makes a category. It argues that it is a mistake to try to completely define categories in advance of empirical investigation, because such definitions are inevitably wrong and then have a pernicious effect on subsequent scientific investigation. Thus, the attempt to describe what categories and concepts are will be based not so much on a prior definition but will reflect research into different types of categories. As we discover new and unexpected kinds of categories that people apparently have, we will have a better understanding of how categories are mentally represented and of what their role is in thought. Having reviewed these examples, the chapter then turns to more controversial cases in which it has been doubted (or could be doubted) whether someone 'has' a category. In particular, this issue arises for young children and nonhuman animals. If our notion of categories derives from work with adult humans, and if subpopulations of humans and other species differ from those adult people in important respects, then there are bound to be psychological differences in their representations of (putative) categories.