  A judgment that DSM categories have insufficient validity led the National Institute of Mental Health to introduce the Research Domain Criteria (RDoC) in grant proposals (Insel et al. 2010). The originators of the RDoC acknowledged that the system entrenched by previous versions of the DSM has increased diagnostic reliability. But they worried that it was too detached from the nature of mental illness, which they conceived of as disorders of brain circuits. For example, rather than existing categories such as depression, the RDoC envisaged a domain of negative valence including symptoms of anxiety or depression that might come to be seen as expressions of an underlying disorder of specific brain circuits (Sanislow et al 2010) . These disorders could be studied at many levels and need not be identified with simple lesions. But future models of mental illness are expected, on this vision, to draw on psychological, neurological, and genetic mechanisms, as well as information about the wider cultural context. In this case, validating a diagnosis is thought of as understanding its underlying causal structure: a diagnosis is valid if it rests on a biological process that can be identified by experiment and observation using the methods of the biological and cognitive sciences. (For philosophical discussion of the RDoC in the context of precision medicine, see Tabb 2020).