Philosopher Ian Hacking assesses the Diagnostic and Statistical Manual of Mental Disorders, the clinicians’ guidebook for psychiatric diagnoses. He finds a fundamental “fatal flaw”:
The first stab at a medical diagnostic manual was made by a friend and exact contemporary of Linnaeus, with the rather daunting name of François Boissier de Sauvages de Lacroix, a physician and botanist in Montpelier. In 1763 Sauvages published his Nosology Methodica, explicitly stating in its title that it was modelled on the classification of plants. He had ten classes of illness, of which the eighth was madness. Each class was divided first into genera and then into species, producing 2400 kinds of malady.
There have been many systems for classifying mental illness since then, but all seem to me to be on the botanical model, and that has been their fatal flaw. …
Sauvages’s dream of classifying mental illness on the model of botany was just as misguided as the plan to classify the chemical elements on the model of botany. There is an amazingly deep organisation of the elements – the periodic table – but it is quite unlike the organisation of plants, which arises ultimately from descent. Linnaean tables of elements (there were plenty) did not represent nature.
The DSM is not a representation of the nature or reality of the varieties of mental illness, and this is a far more radical criticism of it than [National Institute of Mental Health Director Thomas] Insel’s claim that the book lacks ‘validity’. I am saying it is founded on a wrong appreciation of the nature of things. It remains a very useful book for other purposes. It is essential to have something like this for the bureaucratic needs of paying for treatment and assessing prevalence. But for those purposes the changes effected from DSM-IV to DSM-5 were not worth the prodigious labour, committee meetings, fierce and sometimes acrimonious debate involved. I have no idea how much the revision cost, but it is not that much help to clinicians, and the changes do not matter much to the bureaucracies. And trying to get it right, in revision after revision, perpetuates the long-standing idea that, in our present state of knowledge, the recognised varieties of mental illness should neatly sort themselves into tidy blocks, in the way that plants and animals do.