They may be arguing this, but this doesn't make their argument plausible. They are claiming that the brain in synonymous with an abstract concept of the mind (or of the act of thinking). This belief is untenable for many reasons that people have been trying to address for many centuries. Who here has made that argument? I haven't certainly . I'm arguing his presumptions (and yours) are incorrect, not self-serving. The 'chicken or egg' argument is itself specious. There are known neurological conditions that affect behaviour, perception, responses. These tend to have been discovered through the laborious process of science. Beliefs in psychogenic illness, on the other hand are much less safe, both because of the lack of verifiable scientific evidence, and the tendency towards ad hoc literary, even quasi religious theory present in much psychiatric and psycho-analytical discourse. Psychogenic explanations currently are founded on various logical fallacies that Sharpe exhibits even in the examples on this thread: "A causes B therefore B must cause A"; "I don't know what physical mechanism is disordered therefore it must be metaphysical"; The old fallacy of the third way ("It's a little bit of this and a little bit of that", "I've moved beyond dualism. Aren't I clever?"); "I can't decide if you're a faker, a hypochondriac, or your ability to think controls your body in ever increasing ways, therefore I'm going with an eclectic mixture of all three"; "Let's invoke the god of the gaps by the act of balck-boxing"- and so forth. Your use of the word 'purist' is wrong. By your argument, diabetes should be classified as psychological as well. In fact, current attempts are to make everything 'a little bit psychological' in the new DSM (hence the somatic symptoms disorder categorisations). And that is all based on the fallacy of psychogenic diagnosis by default in areas of uncertainty in medical knowledge. The argument against so-called 'purism' is actually an argument against clarity and logic (I'd also say scientific method). I note you have not addressed the fact the psychs are so desperate to classify ME/CFS in F48.