Theories of natural kinds can be seen to face a twofold task: First, they should provide an ontological account of what kinds of (fundamental) things there are, what exists. The second task is an epistemological one, accounting for the inductive reliability of acceptable scientific concepts. In this chapter I examine whether concepts and categories used in the cognitive sciences should be understood as natural kinds. By using examples from human memory research to illustrate my argument, I critically examine some of (...) the main contenders for a theory of natural kinds. I show that when applied to complex target domains – such as human cognition – both essentialist theories and more liberal accounts of natural kindhood (such as HPC theory) fail to simultaneously satisfy the ontological and epistemological desiderata for a theory of natural kinds. I argue, however, that natural kindhood of a category in a metaphysical sense is not necessary for its inductive reliability, and that HPC theory provides an analytically useful account of the grounds of category-based inductive inference. (shrink)