The central question in this book is why it seems reasonable to divide up the world in one way rather than another, or what the rational basis is for our language to contain certain kinds of general words rather than others. In the course of the exploration of this question, a broad range of metaphysical and epistemological topics is covered, including projectibility and similarity, natural properties and things, the structure of 'fine-grained' propositions, and the relevance of such pragmatic notions as salience and economy.