But, contrary to popular belief, the relationship between madness and truth is a complex one. They are made out to be strangers but often they are more like distant cousins.
This relationship has recently been acknowledged with the publication of the new version of the psychiatrists’ diagnostic manual (the DSM-5) where one of the most interesting but less noticed changes has been the redefinition of the delusion, a symptom that has long been considered the “basic characteristic of madness”.
Delusions, in the medical sense, are not simply a case of being mistaken, as the everyday use of the term suggests. They are profound and intensely held beliefs that seem barely swayed by evidence to the contrary – even to the point of believing in the bizarre. My heart has been replaced by steam. My thoughts are being stolen by satellites. The government communicates with me through birdsong.
But many delusions are not outlandishly eccentric, they are simply implausible. Consider the scenario where people believe that their neighbours are conspiring against them or that they are the subject of a film star’s secret affections. Occasionally, these beliefs turn out to be true, but this is not a reliable guide to whether someone is delusional or not. This was memorably illustrated by the psychiatrist Andrew Sims, who warned in his psychopathology textbook Symptoms in the Mind that spouses of people with delusions of infidelity may occasionally be driven to infidelity. This romantic betrayal does not suddenly cure their partner of their mental illness.
The general idea is that delusions represent a problem with how you believe – that is, a problem with forming and changing beliefs – not a problem with what you believe. In other words, simply believing something strange or unusual should not be considered a problem but having “stuck” beliefs that are completely impervious to reality suggests something is mentally awry.
Instead, the new definition of delusions describes them as fixed beliefs that are unswayed by clear or reasonable contradictory evidence, which are held with great conviction and are likely to share the common themes of psychosis: paranoia, grandiosity, bodily changes and so on. The belief being false is no longer central and this step forward makes it less likely that uncomfortable claims can be dismissed as signs of madness.
This is relevant to my blogging because I blog about Bayes Theorem and cognitive science within the context of religious history and beliefs. If someone is completely impervious to updating their beliefs based on new evidence, then this new DSM model suggests that they are leaning towards being delusional. This is kind of tricky territory because this implies that any belief that is unfalsifiable should be considered as a type of delusion.
Of course, in the common lexicon an unfalsifiable belief is simply a social faux pas of the scientific method. But as I’ve written pretty recently, falsifiability is not just a faux pas of the social process of the scientific method, but follows necessarily from being able to update your beliefs rationally.