Recently there has been a trend of moving towards biological and neurocognitive based classifications of mental disorders that is motivated by a dissatisfaction with the syndrome- based classifications of mental disorders. The Research Domain Criteria (indicated with the acronym RDoC) represents a bold and systematic attempt to foster this advancement. However, RDoC faces theoretical and conceptual issues that need to be addressed. Some of these difficulties emerge when we reflect on the plausible reading of the slogan “mental disorders are brain disorders”, that according to proponents of RDoC constitutes one of its main presuppositions. Some authors think that endorsing this idea commits RDoC to a form of biological reductionism. We offer empirical and theoretical considerations for concluding that the slogan above should not be read as a reductionist thesis. We argue, instead, that the slogan has a pragmatic function whose aim is to direct research in psychopathology. We show how this function might be captured in the framework of a Carnapian explication as a methodological tool for conceptual engineering. Thus, we argue that a charitable interpretation of the aims of the proponents of RDoC should be understood as an attempt at providing an explication of the concept of mental disorder in terms of brain disorder whose main goal is to provide a more precise and fruitful notion that is expected to have a beneficial impact on classification, research, and treatment of psychiatric conditions.