Skip to main content

Taxonomising Delusions


Colin Klein

We are philosophers working on various topics that intersect with delusions. Colin Klein works on the philosophy of neuroscience and the application of interventionist accounts of causation to this area, and has also discussed the relation between psychopathologies like somatoparaphenia and his theory of pain. Stephen Gadsby works on distorted body representations and false body size beliefs in anorexia nervosa. And Peter Clutton has defended the doxastic status of delusions—offering a cognitive phenomenological account of delusions (forthcoming)—and explored the status of delusions on the harmful dysfunction account.


Peter Clutton

Any discussion of delusions needs some criteria by which patients are grouped together as having the same delusion. In our paper, ‘Taxonomising Delusions: content or aetiology?’, we compare content-based and aetiological taxonomies of delusions, arguing in favour of the latter.


Stephen Gadsby


Most authors taxonomise delusions by the content of the delusional belief: Capgras patients believe that their spouse has been replaced by an imposter, Cotard’s delusion involves the belief that one is dead, and so on. Taxonomising by belief content has intuitive appeal. Content is often what brings patients to clinical attention in the first place, and may be all a researcher has to work with. Additionally, content appears to offer a theory-neutral starting point, in that it does not presuppose any particular theoretical explanation of the underlying causes of delusions.

We argue that these intuitive advantages are not as strong as they seem, and that an aetiological taxonomy is to be preferred: that is, we think that patients ought to be grouped by the causes of their delusions, rather than by what they believe. An aetiological taxonomy has the advantage of supporting the kinds of empirical generalisations we want from scientific taxonomies. Good taxonomies identify similarities among group members that manifest across a variety of distinct circumstances. In studying the cognitive processes that lead to delusions (and thereby learning about the normal processes of cognition, as cognitive neuropsychiatrists aim to do), we want discoveries about one patient to guide our thinking about other patients we encounter with the same problem. Taxonomising delusions by their underlying cognitive causes allows for just such projectability.

Further, we argue that content-based taxonomies cannot be truly theory-neutral. For example, why do we group together those who believe their spouses have been replaced by an imposter? Is it the personal relation aspect that is important (i.e spouse)? If so, do we extend that to other close loved ones? What about pets, plants, objects, or oneself in the mirror? In so far as content-based approaches have answers to these questions, we think it is only to the extent that they smuggle in aetiological thinking: one might suspect, for example, that face perception plays a role in some of these delusions, and thus group spouses, friends, and maybe pets, but exclude objects and plants. Aetiology is thus smuggled in the back door.

The aetiological approach we advocate might recommend the lumping and splitting of many of the traditional content-based groupings. We give evidence, for example, that somatoparaphrenia is causally heterogenous: it can arise from paralysis, breakdowns in the sense of bodily ownership (itself a heterogenous phenomenon), and depersonalisation. Each of these causal antecedents ought to be distinguished for theoretical purposes: aside from consequences of the shared belief, there is no reason to believe that discoveries about a paralysed patient would generalise to a depersonalised one. If so, then there is no somatoparaphrenia per se, only the somatoparaphrenias. Conversely, we argue that some content-based groupings are arbitrarily narrow, and so may miss important generalisations.

The consequences of this view are further fleshed out in terms of an interventionist account of causation. We explore how the taxonomic process might proceed, emphasising that it is likely to be an ongoing, iterative process. We should expect this process of refinement to provide significantly more useful categories of delusions, even if they do not correspond neatly to the beliefs that seem to distinguish the patients who have them.

Labels:

Popular posts from this blog

Delusions in the DSM 5

This post is by Lisa Bortolotti. How has the definition of delusions changed in the DSM 5? Here are some first impressions. In the DSM-IV (Glossary) delusions were defined as follows: Delusion. A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person's culture or subculture (e.g., it is not an article of religious faith). When a false belief involves a value judgment, it is regarded as a delusion only when the judgment is so extreme as to defy credibility.
Read more

Motivated Reasoning in Science

Today's post is by Josh May (University of Alabama, Birmingham). In this post, he talks about one of his papers published in Synthese and entitled " Bias in Science ". Josh May Much discussion of the replication crisis in science has focused on the social sciences, particularly psychology. A common narrative is that the social sciences are particularly susceptible to powerful biases, such as moral and political ideology. I argue instead for a parity thesis: all areas of science are subject to bias, through the general psychological mechanism of motivated reasoning . This provides a unified framework for understanding how values influence the entire scientific enterprise. The scientific process involves numerous decisions that can be influenced by one's values--including moral, political, and prudential values--which manifest as goals or motivations. A researcher wants badly, say, to publish in a prestigious journal in order to either advance her career or maintain ...
Read more

Models of Madness

In today's post John Read  (in the picture above) presents the recent book he co-authored with Jacqui Dillon , titled Models of Madness: Psychological, Social and Biological Approaches to Psychosis. My name is John Read. After 20 years working as a Clinical Psychologist and manager of mental health services in the UK and the USA, mostly with people experiencing psychosis, I joined the University of Auckland, New Zealand, in 1994. There I published over 100 papers in research journals, primarily on the relationship between adverse life events (e.g., child abuse/neglect, poverty etc.) and psychosis. I also research the negative effects of bio-genetic causal explanations on prejudice, and the role of the pharmaceutical industry in mental health. In February I moved to Melbourne and I now work at Swinburne University of Technology.  I am on the on the Executive Committee of the International Society for Psychological and Social Approaches to Psychosis and am the Editor...
Read more