The study of category organization has emphasized that categories in the middle level of a taxonomic hierarchy tend to be highly differentiated in that they have both high levels of within category similarity and low levels of between category similarity. Recent work in similarity reveals a distinction between pairs of categories that are seen as dissimilar because they have few commonalities and pairs of categories that are seen as dissimilar because they have many psychologically relevant differences. We suggest that the low betwen category similarity proposed for neighboring basic level categories is actually a matter of having many psychologically relevant differences. In contrast, the low betwen category similarity of superordinates is a result of their having few commonalities. We evaluate this claim using a variety of natural stimuli and converging measures. An initial study focuses on the contrast categories that people generate for categories at different levels of abstraction. Two additional studies examine the commonalities and differences that people produce for pairs of categories. A final study focuses on the effect of comparability on the use of categories by examining differences in the strategies used to combine concepts at different levels of abstraction. We discuss the results in terms of current views and models of the basic level.