In contemporary psychotherapy, we often hear that “diagnosis does not replace formulation.” This is true, but it is only half the story. It is equally true that formulation does not replace diagnosis. These two activities answer different clinical questions and rely on different kinds of knowledge. When they are conflated, clinical thinking quickly becomes muddled, and treatment often suffers. The problem is not that formulation is emphasized too much. It is that diagnosis is increasingly treated as optional or even dispensable. This represents a fundamental misunderstanding of what diagnosis actually is. What Is Psychiatric Diagnosis? Diagnosis is a descriptive and phenomenological act. It is grounded in the form of symptoms, their patterning, and longitudinal course. It answers the question: What kind of illness is present? This mode of thinking belongs to the domain of explanation (Erklären) and to the natural-scientific tradition in psychiatry. It was articulated most clearly by Emil Kraepelin and later by Karl Jaspers. Diagnosis, in this sense, is necessarily resistant to speculative narratives. It does not ask why a patient is ill …