Although researchers in psychiatry have been trying for decades to elucidate the pathophysiology underlying mental disorders, relatively little progress has been made. One explanation for this failure is that diagnostic categories in psychiatry are unlikely to track underlying neurological mechanisms. Because of this, the US National Institutes of Mental Health has recently developed a novel ontology to guide research in biological psychiatry: the Research Domain Criteria. In this paper, I argue that while RDoC may lead to better neuroscientific explanations for (...) mental disorders, it is unlikely that this new knowledge will then lead to an improved diagnostic system. I therefore suggest that researchers in psychiatry should work toward the development of two new ontologies: one for research and one for clinical practice. (shrink)