What kinds of “things” are “women,” “men,” and gender? How can we best conceptualize these entities in order to produce good psychological knowledge? One way is to think about the “things” that women and men are as intrinsically different from each other. Other ways of conceptualizing women and men do not point to differences. Instead they focus on social hierarchies between men and women; that is, how men and women often are positioned unequally in the social structures they inhabit. Yet other ways of conceptualizing men and women and gender, such as those ways put forward by queer theorists and transgender theorists, reject entirely the idea of two distinct and enduring sex categories.

Sorting the world into categories is necessary in order to produce knowledge about anything. Knowers need to be able to say, for instance, whether two objects are similar or different. To be able to do this, they need to think in terms of categories. A category is a set of objects that share certain characteristics. “Dog,” for example, is such a category. Knowers also need to be able to specify what differs between the categories that they have identified. For example, what features of the category “cat” distinguish it from the category “dog”?