Psychiatric Disorders, Multifactorialism, and Kinds

Today I attended and talked at a great symposium called “What Kinds of Things Are Psychiatric Disorders?” organised by the University Center of Psychiatry at Groningen. The guest of honour was Kenneth Kendler, who gave a long, wide-ranging, and thoroughly excellent talk about the reality or otherwise of the psychiatric disorders captured by the DSM. It was one of the best talks I have heard in a long time, and philosophically more astute than many talks by self-identifying philosophers (including myself). The position he outlined got me thinking about a number of issues in the philosophy of epidemiology and of medicine.

He begins by arguing that realism about psychiatric disorders cannot be modelled on realism about physical kinds: it cannot be like realism about the periodic table. At best it would need to be like realism about biological species – acknowledging the lack of essential properties, the fuzzy boundaries, and so forth. His own view, however, is that realism of even this moderate kind is not warranted about psychiatric disease kinds, at least not those in the DSM. Part of his argument is a pessimistic induction from past psychiatric diagnoses that are no longer recognised. The other part comes from the massive multifactorialism of psychiatric disorders.

One interesting thing about this view is that it also applies to multifactorial diseases outside psychiatry – cancer, for example. The same considerations apply – both the mutlifactorialism, and the pessimistic view of the durability of our current classifications. The two arguments interact, perhaps: massive multifactorialism means that we do not have a good general explanation of why a given set of symptoms occurs, and this lack of explanation indicates that we don’t understand the phenomenon very well and thus that we are quite likely to be wrong about it in some yet-to-be-discovered ways.

Kendler’s view of illness in general, however, is not constructivist. He combines a sceptical stance towards the kinds in the DSM with a realist-leaning pragmatism about psychiatric disorder, the overarching thing, as opposed to the ways we have cut it up. In other words, he thinks that psychiatric illness is a real thing; but he is sceptical about our way of individuating psychiatric diseases. So, at least, I understood his position.

This view also connects in interesting ways with the debate about health in the philosophy of medicine. In that debate, “realism” is not used – instead, “naturalism” is the closest correlate. It is not an equivalent, however, since a naturalist typically denies that there is any normative component to health facts, while Kendler – in response to an acute question from the audience – thinks that health is fundamentally about human goals and suffering, and thus fundamentally normative. The naturalism/normativist debate elides two dimensions of disagreement, one concerning the objectivity of health facts (on which Kendler is a pragmatist, but towards the objective end of the spectrum, opposed to so-called normativists in the health debate), the other concerning whether health is value-laden (on which Kendler appears to be with with the normativists). I have thought for a while that it should be possible to occupy a position like this – agreeing with naturalists on one dimension of disagreement, normativists on another – and I’m pleased to have found someone who does, and someone so credible.

The picture, then, is of a spectrum of disorder which is fairly independent of us, and also normative, but which is fairly arbitrarily cut up by us in our attempts to understand it. That’s a crude summary, of course. But it made me wonder if an exact reverse might also be attractive. Some disease kinds, especially infectious diseases, might suit realism of the kind we might have about biological species. After all, infectious diseases correspond to actual biological species, or something similar enough. Thus we might be (fairly) realist about cholera – it’s what happens when something we are fairly realist about (vibrio cholerae) gets into the small intestine of something else that we are fairly realist about (us). However, we might be irrealist, or less than realist, about health facts in general – not just psychiatric health and disease, but health and disease in general. We might think that health is not a fundamental category – not a kind, not even in the way that species are kinds – and yet think that certain diseases do count as kinds.

I am not sure where this leads, but my hope would be to develop a notion of health and illness – the mere absence of health – as secondary properties, like colour, which depend in non-arbitrary non-contingent ways on us (as opposed to a constructivist stance, which makes facts depend on us in contingent ways). Such a view may make room in the picture for the diagnoser as well as the diagnosed, and it may explain why a particular set of objective characteristics seem to us to belong together as “health” or as a given illness, despite the fact we often find little objective to bundle them together. Perhaps it also would answer to Kendler’s pragmatist intuitions, which I also find very compelling.

Whatever the prospects for Kendler’s view or for this hastily-sketched alternative, the lecture really helped me pull together a number of these issues. It left me thinking that the overarching goal for contemporary philosophical work on the nature of health and disease must be to link the debates about the status of health (naturalism, normativism, and all that) with debates about the status of disease kinds and with the literature on natural kinds more generally. Kendler’s excellent talk today embarked on this extremely complex task and went a remarkable way towards offering a comprehensive and plausible position.

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