Wednesday, 18 November 2015

Kendler’s ‘Toward a limited realism for psychiatric nosology based on the coherence theory of truth’

Some of our philosophy and mental health students have been looking at Kenneth Kendler’s paper ‘Toward a limited realism for psychiatric nosology based on the coherence theory of truth’ prompting me to look at it. It is odd. I think my confusion is more psychological than philosophical, however.

The paper unleashes the meta-induction. Most past theories have proved to be false and most theoretical terms did not successfully refer. Thus, by induction, most of our current theories will prove to be false and have non-referring theoretical terms. What makes this a particularly poignant argument is that it deploys a form of inference widely assumed to play a key role in science against science. Kendler summarises this thus:

In discussions for and against scientific realism, strong support for the instrumentalist position has come from what has been called the ‘pessimistic induction’ (PI) argument (Psillos, 1996). Considering the history of scientific theories in any particular discipline (e.g. astronomy, genetics, physics, psychology), over time, older theories have continuously been replaced by newer ones. This in fact often defines scientific progress. Thus, sitting in the present, we can look back at earlier theories, since replaced, and see entities and processes referred to by these theories that are no longer considered to be real. For example, planets do not travel in epicycles as they circle the earth, ether does not exist and inheritance is not (typically) Lamarckian in nature. [Kendler 2015: 1115]

He then goes on to list a number of non-referring theoretical terms from the history of science originally set out by Larry Laudan. This then motivates an application of the meta-induction to psychiatry. Kendler comments:

Anyone with a smattering of knowledge of psychiatric history would have little problem in creating a list of 12 abandoned psychiatric disorders that at one time were widely used and considered true but are no longer considered useful and would perhaps be judged to be ‘false’. One such list would be: (i) paraphrenia; (ii) neurasthenia; (iii) phrenzy; (iv) periodic hallucinatory insanity; (v) drapetomania (Cartwright, 2004); (vi) monomania (Esquirol, 1845); (vii) lypemania (Esquirol, 1845); (viii) demonomania (Esquirol, 1845); (ix) anxiety-happiness psychosis (Leonhard, 1979); (x) cataphasia, (Leonhard, 1979); (xi) confabulatory euphoria (Leonhard, 1979); and (xii) hysteria. The PI argument applied to current psychiatric disorders argues strongly against what might be called a ‘hard’ realism model for psychiatric disorders. [ibid: 1116]

In the face of this Kendler makes two suggestions. The first is that whilst particular diagnostic categories may prove mistaken, the idea that there are some real psychiatric illnesses looks more secure. ‘we can be much more confident about the existence of the liquid than the particular bottles in which it is now residing’. Strangely there does not seem to be much of an argument for this and to defuse the meta-induction. I am sure he is right but I think we need to be told why the inductive inference can rationally be expected to fail on this point. Earlier, in an apparent spirit of fairness, Kendler mentions Putnam’s no miracles argument for scientific realism. But he does not mention it again nor does he investigate whether it could apply to some areas of science but not others nor how it intersects with the meta-induction.

Second, he suggests that we should adopt a particular view of truth with respect to psychiatric theory.

The standard approach to truth is the ‘correspondence theory’, which assumes that a statement (or theory) is true if it corresponds to a stable, mind-independent reality. This is a plausible way to think about the elements of the periodic table, but it is poor way to think about psychiatric disorders. [ibid: 1117]

Again, there is no diagnostic move to explain why the Periodic Table is exempt from the meta-induction and hence merits a correspondence approach. But:

For psychiatric disorders, we need a less ambitious version of reality. A humbler approach can be found in the coherence theory of truth. This theory postulates that something is true when it fits well with the other things we know confidently about the world. [ibid: 1117]

And then a little later we have the application of this to psychiatry:

What do we mean in this metaphorical space when we want to say that a diagnosis is ‘real’? Before answering that, let’s consider the simpler question: ‘What do we mean in this metaphorical space when we want to say that one diagnostic concept is more real than another?’ Here, the answer is simple. To be more real means to be connected to more already existing pieces and/or to be connected by stronger strings. So what then do we mean to say a diagnosis is real? We might say it is ‘pretty well’ connected with the other pieces, that it is ‘pretty well’ integrated into our accumulating scientific data base. In other words, a diagnosis is real to the degree that it ‘coheres’ well with what we already know empirically and feel confident about. [ibid: 1117]

The idea seems to be that some areas of reality and some claims as to truth are governed by one kind of truth and others governed by another. Note that this isn’t saying that the kinds of facts vary – which one might think for, say, the facts expressed in moral claims by contrast with natural scientific claims – so much as that the kind of truth varies. A redundancy theorist of truth, for example, might, also for example, think that understanding or grasping moral facts requires a special design of mind whilst grasping physical facts does not. Different ontologies, same conception of truth. This is not Kendler's way. The benchmark for psychiatry is just lower/humbler than for chemistry. What it is for something to be true in psychiatry is not just differently constituted (for example in a mind-dependent way) but actually easier. To call something true for psychiatry should involve less than for chemistry.

But the reason my confusion is more psychological than philosophical is that I cannot believe that Kendler really believes any of this. That is, that saying that schizophrenia exists is somehow making a quite different kind of linguistic move (disciplined differently as a move) than saying plutonium exists ie measured against the world differently. Surely he doesn’t think that one can just pick theories of truth willy nilly? In reply to a suggestion (by PZ) that this worry presupposes a hostility (by me) to a coherence theory of truth, I do not think so. I would be happy to take a coherence theory seriously - I used to be a Davidsonian, after all - but not a pick and mix attitude to theories of truth. Surely if one thinks a coherence theory is true then it sets the standard for truth, punkt. It doesn't set what one concedes is a lesser standard.

And against what standard could a theory of truth be ‘humbler’? Is the truth of the coherence theory of truth itself a matter of correspondence or coherence? My hunch is that talk of ‘humbler’ implies that Kendler thinks that the truth of this meta-question is really truth as correspondence. But that in turn suggests that truth generally is really correspondence and the local adoption of coherence isn’t serious. It’s just a way of speaking.

If so, I don’t understand why anyone would think that serious worries about the validity of disease categories could be lanced by playing with theories of truth. So at the psychological level, I cannot believe that Kendler really believes in a mere coherence theory of truth and hence I cannot see how that could thus provide genuine solace for real worries about psychiatric taxonomy. That all seems too easy. So why did he write it?

Kendler, K. (2015)‘Toward a limited realism for psychiatric nosology based on the coherence theory of truth’ Psychological Medicine (2015), 45, 1115–1118