The term „illness” implies a medical disease model, namely that symptoms or syndromes indicate an underlying organic disease - in the case of psychiatry a disorder of the brain. But no brain markers could be identified until today, which would indicate a psychiatric illness or in particular a certain psychiatric illness. Furthermore organic causes of a mental disorder are an exclusion criterion for a diagnosis of a mental disorder. For all these reasons all international classifications systems use the term “disorder” instead of “illness”.

Beyond the question if mental disorders are disorders of the brain one might challenge the concept of psychiatric diagnoses at all. Most diagnostic thresholds are arbitrary or imposed on pragmatic grounds. For a categorical diagnosis to be scientifically valid, clear symptom boundaries should separate it from other conditions. But this is rarely the case concerning psychiatric diagnoses.

In many respects a dimensional approach would be much more appropriate than a categorical view. A dimensional approach would reflect the fact that mental problems are part of the human condition, which turn into psychiatric disorders when the affected individual cannot perform his or her social roles any longer.

The personal, social and environmental factors that determine mental health and mental illness may be clustered conceptually around themes like the development and maintenance of healthy communities and each person's ability to deal with the social world and manage his or her life. All this would be much more helpful than the conceptualisation of mental disorders as brain diseases.