On Diagnosis and Formulation
Formulation does not replace diagnosis but is instead dependent on it.
Updated March 5, 2026 | Reviewed by Gary Drevitch
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 isn't. 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 in a biographical or historical sense; it asks what the illness is, based on observable phenomena and their evolution over time.
In modern psychiatry and psychopathology, this tradition was restored in the 1970s by psychiatrists at Washington University in St. Louis, particularly Eli Robins and Samuel Guze, whose work was instrumental in the development of DSM -III .
This should not be taken to imply that all DSM diagnoses represent valid diseases or conditions . Many categories remain provisional, weakly validated, or have been proven invalid. Yet the fallibility of specific classifications does not obviate the need for diagnostic reasoning.
Formulation belongs to a different domain: understanding ( Verstehen ). It is concerned with the patient's subjective experience of illness—their life history, developmental trajectory, personal meanings, and interpersonal relationships. Formulation asks a different question: How can we make sense of why this person is ill?
This approach belongs to the interpretive traditions of psychoanalysis and existential psychology, in which the clinician's task is not primarily to classify illness but to understand the patient's subjective world and life history.
These considerations are indispensable to humane and effective clinical care. They help us understand how symptoms develop, are experienced, defended against, and embedded in relationships. But formulation does not determine diagnosis, nor can it substitute for it. A detailed narrative does not establish a diagnosis, and psychological understanding does not define the nature of a disease or psychiatric condition.
Diagnosis Is the Basis for Formulation
It is a generally accepted tenet of scientific medicine that diagnosis comes before treatment. One must first know what one is dealing with before attempting to understand why it has taken a particular shape in a particular person.
Sometimes the patient has a biological disease (such as manic -depressive illness or schizophrenia). Other times, it is a problem with significant environmental etiology (such as posttraumatic stress disorder or borderline personality disorder ). Either way, diagnosis is the necessary starting point for understanding the nature of the patient's particular problem.
Take, for instance, depressed mood. It is important to know whether symptoms are severe, episodic, and marked by psychomotor slowing (indicative of melancholic depression , which requires biological treatment) or if they are chronic, low-grade, mixed with anxiety , or interpersonally mediated (indicative of nonmelancholic depression or a personality disorder, necessitating psychotherapy). The importance of diagnosis becomes even clearer if the depression is caused by a neurological disease, such as a brain tumor.
In each case, diagnosis informs formulation. Psychological theories of depression may be particularly relevant if the depressive symptoms occur in the context of a personality disorder, but they do not explain melancholia, whose etiology is biological. The same is true of depressive syndromes caused by neurological disease. In such conditions psychotherapy may still be helpful, but its role is supportive or adaptive rather than explanatory.
When clinicians are taught formulation without diagnosis, the result is often a kind of free-floating narrative, untethered from the realities of psychopathology. Formulation becomes a substitute for classification rather than a complement to it, and clinical reasoning drifts toward explanation without first establishing what is being explained.
Only when diagnosis establishes what the condition is can formulation illuminate how it is experienced, ensuring that clinical understanding remains both scientifically anchored and humanly meaningful.
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Mark L. Ruffalo, LCSW, is an Assistant Professor of Psychiatry at the University of Central Florida College of Medicine and Adjunct Assistant Professor of Psychiatry at Tufts University School of Medicine.
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