A central aspect of people's beliefs about the mind is that mental activities--for example, thinking, reasoning, and problem solving-- are interrelated, with some activities being kinds or parts of others. In common-sense psychology, reasoning is a kind of thinking and reasoning is part of problem solving. People's conceptions of these mental kinds and parts can furnish clues to the ordinary meaning of these terms and to the differences between folk and scientific psychology. In this article, we use a new technique for deriving partial orders to analyze subjects' decisions about whether one mental activity is a kind or part of another. The resulting taxonomies and partonomies differ from those of common object categories in exhibiting a converse relation in this domain: One mental activity is a part of another if the second is a kind of the first. The derived taxonomies and partonomies also allow us to predict results from further experiments that examine subjects' memory for these activities, their ratings of the activities' importance, and their judgements about whether there could be "possible minds" that possess some of the activities but not others.