Although both the generalizing or nomological and the individualizing or idiographic approaches are currently widely considered as necessary components of a comprehensive approach to psychiatric diagnosis, no satisfactory answer to the problem of their mutual articulation is still in sight. Worse still, it has been convincingly argued that strictly individualizing statements are impossible. This paper explores the possibility of their mutual integration within a synthetic approach. Multiple-domain, comprehensive diagnostic assessments of individual mental patients constitute the idiographic component of this approach, whereas the law-like generalizations associated with each of these assessments is the nomothetic component. By integrating multiple diagnostic assessments with their associated law-like generalizations, this synthetic approach can account for individual mental patients’ major particularities at all main levels of their existence—biological, psychological and social—and in all major domains of psychiatric expertise—descriptive, explanatory, predictive, and therapeutic. Accordingly, the approach outlined herein can help bridge to some considerable extent, moreover in a principled and rigorous manner, the gap between the generality of psychiatric knowledge—whether descriptive, explanatory, predictive, or therapeutic—and the numerous particularities of individual mental patients, biological, psychological, and/or social ones. By the same token, this approach helps to bridge the alleged methodological gap between the natural and the human sciences and promotes the unification and mutual integration of psychobiological and psychosocial parts of psychiatric knowledge. In turn, the systematization of the whole of psychiatric knowledge facilitates its integral application by clinicians in the service of their individual patients.