Diagnosis and formulation answer different questions; neither can substitute for the other.

Diagnosis identifies what illness is present; formulation explains why it takes this form in this person.

Sound formulation depends on diagnosis to anchor understanding in the realities of psychopathology.

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 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 the DSM-III.

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 psychological 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.

When clinicians are taught formulation without diagnosis, the result is often a kind of free-floating narrative, untethered from the science 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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