'Understanding it makes it normal': is it a reasoning fallacy or not?

In 1973, P. Meehl drew attention to the fact that some clinicians tend to interpret the otherwise clear symptomatic behaviour of their patients as 'normal' if they are given a plausible causal story of patients' behaviours. He claimed that this way of thinking is, in fact, fallacious and gave the alleged fallacy the 'catchy' name 'understanding it makes it normal'. Thirty years later, the cognitive psychologists W.K. Ahn, L. Novick and N. Kim questioned the fallacy status of 'understanding it makes it normal' by arguing that this way of reasoning is not only quite common among clinicians but that it is in fact rational. The controversy over whether 'understanding it makes it normal' is a reasoning fallacy or not is still unresolved and this is evident from the recent discussion about the proposed removal of the 'normal grief' exclusion criterion for Major Depressive Disorder from DSM-5. This paper proposes an analysis of what stands behind the two opposing claims about 'understanding it makes it normal'. The analysis builds on the distinction between validity and utility of psychiatric diagnoses and reaches the following conclusions: (1) the fallacy claim is consistent with the assumption that the psychiatric diagnoses are valid descriptions of real mental disorders; (2) the non-fallacy claim is consistent with the opposite assumption that current psychiatric diagnoses are not valid but only useful descriptions and their utility varies across different contexts; (3) if we agree that there is not enough evidence for the validity of the diagnostic categories embedded in DSM-4 and ICD-10, we should also agree that the behaviour of those mental health professionals who change their diagnoses under the influence of the causal context is rational; (4) nevertheless, the 'understanding it makes it normal' reasoning strategy should be considered a bias insofar as it takes into account only part of the causal context: the causes of the symptoms but not what they themselves might cause. The neglect of the latter might have dramatic negative consequences in clinical practice. In addition, some recent studies suggest that this bias probably has cultural roots.