Not everything has joints
As I noted in my previous book, The New Laws of Psychology, the ancient Greek philosopher Plato once suggested that natural science was the art of 'carving nature at its joints'. Plato said a lot of things, some of which were actually nonsense. What he meant by this particular phrase was that scientists need to identify and classify the phenomena - the birds, animals, plants and insects, the minerals, elements and forces - that shape the natural world. The idea of creating order out of chaos is seductive, and scientists in many branches of science - geology, botany and biology in particular - have always had a strong emphasis on classification.
The process of assigning a mental health 'diagnosis' is essentially one of classification. This kind of classification has a double attraction for psychiatry. Firstly, as a standard methodology within science and medicine, it is pleasingly 'scientific'. Psychiatry, in particular, occasionally appears rather sensitive to accusations of being unscientific. Secondly, for a while, classification appeared to offer some benefit.
Johann Reil first used the term 'psychiatry' in 1808. The 19th century saw huge leaps forward in medical understanding and skills, just as it saw progress across society. One of the particular leaps forward related to the classification of diseases, drawing on new knowledge of physiology and infection and based on scientific principles. The progress in medical practice is undeniable. And early psychiatrists were faced with the same challenges as modern psychiatrists. They were caring for large numbers of very distressed patients with complicated, ever changing, problems in a context of great social change and significant deprivation. The classification and definition of what is now called 'schizophrenia' was largely influenced by the work of the psychiatrist Emil Kraepelin. In 1919, Kraepelin suggested that the confusing and distressing chaos of the problems he was trying to address in his hospital role could be simplified by classifying them into two broad illnesses: 'dementia praecox' (Latin for loss of intelligence before the onset of old-age, a term later replaced by 'schizophrenia') and 'manic-depression'.2
We are still living with this legacy. In the field of medical science as applied to physical health, this is a treasure - we are hugely fortunate, today, that doctors can identify infections and pathologies of physiology from their opaque symptoms, aided by diagnostic laboratory tests. But, in my opinion, Plato's dictum does not apply well to problems of human emotion. I accept that 'carving nature at the joints' has great applicability in physical medicine, but Platonic quotes are not always scientifically valid. Plato, for instance, also said that there were three kinds of men (he didn't mention women), men of gold, men of silver and men of bronze. He used this to justify social hierarchies, segregation, exploitation and slavery ... while admitting it was a 'noble lie'. So I don't accept everything Plato says (in fact, I tend to follow the advice of Roger Bacon from the 15th century, who advised people not to follow the advice of those in positions of authority merely because of their station ... and got himself excommunicated as a result). And when we look at the classification of human distress, we need to be equally critical. If classification depends on 'carving nature at its joints', where are those 'joints'? In fact, are there any 'joints' at all? Is it actually ever possible to make those kinds of categorical decisions in the field of mental health? I sometimes use the rather silly analogy of a chicken and a sausage - we can carve a chicken at the joints, but a sausage has no joints. I think mental health is a sausage, not a chicken. It simply doesn't have these joints.
Of course, if psychiatric diagnoses were valid, then the classification of mental disorders could lead to progress, just as it has in physical health. It would allow the causes and origins of real 'disorders' to be understood. If we could reliably and validly identify a group of people with a particular disorder, we could examine their medical status or life histories to reveal a particular brain abnormality, a particular biochemical imbalance, a particular set of experiences or a particular pattern of thinking which could then explain the origins of that particular disorder. Since this has been successful in other branches of medicine, it makes sense to assume it could work in psychiatry. The problem is it just simply doesn't appear to work that way.