This chapter sets out the broad metaphysical picture that guides the inquiry. I derive a naturalist notion of kinds from the nineteenth-century discussion of classification and kinds initiated by Whewell, Mill, and Venn, rather than the more recent essentialist view of natural kinds suggested by Kripke and Putnam. I go on to defend a “simple causal theory” of cognitive kinds, which conceives of them as “nodes in causal networks” in the cognitive domain. In addition, I argue against the layer-cake picture of scientific domains and put forward some reasons to resist reductionism when it comes to cognitive categories, based on different bases for individuating cognitive and neural categories. Finally, I respond to some concerns that the resulting ontological picture is not a realist one, on the grounds that it countenances the existence of cognitive kinds that are mind-dependent and self-reflexive.