Richard Sykes (2002, this issue) wants to convince psychiatrists that chronic fatigue syndrome (CFS)/myalgic encephalomyelitis (ME) is a ‘physical’ illness, and also convince them that patients presenting with this syndrome should normally be regarded as suffering from a ‘physical disablement’, and thus be eligible for the full mobility component of the Benefits Agency's disability living allowance. In fact, there is no need to worry about the disability living allowance. This is a purely administrative issue which, as he says, has already been conceded by the Benefits Agency. But in order to convince psychiatrists that CSF is a physical disorder, he feels that he has to rebut the argument that the distinction between mental and physical is ‘meaningless’.

I assume that I have been invited to comment on his article because I recently argued that the distinction between mental and physical illness is ill-founded and incompatible with contemporary understanding of disease, and that it is high time we abandoned it (Reference KendellKendell, 2001).

Sykes is quite right to point out that the distinction between physical and mental illness is in widespread use and has far-reaching effects. (He is also right that some naïve doctors assume that a patient's symptoms must be psychogenic if they cannot find a physical cause for them.) It is true, therefore, that the distinction is still meaningful to the lay public and to some doctors. The crucial issue, though, is not whether the distinction is meaningful to some people but whether it is soundly based or misleading.

As others have done, I have argued that the historical assumptions on which the distinction between mental and physical diseases was based have been discredited and that it is increasingly clear that there is no fundamental difference between them. Both somatic and psychological symptoms have a somatic substrate, psychological and social factors often contribute to aetiology and influence outcome in both physical and mental illnesses, and psychological and social therapies may have an important role in the treatment of both. As a result, the assumptions that are commonly made about so-called mental illnesses – that they are fundamentally different from all other kinds of illness, that they are due to a lack of self-control or will power, and therefore less deserving of treatment and sympathy – are unjustified and misleading.

Two generations ago, it was widely assumed that anthropologists and laymen could distinguish several different human races and that there were important physical, intellectual and moral differences between them. The scientific basis for those assumptions and beliefs has now been eroded, most recently and conclusively by the human genome project. But although the scientific basis of the concept of race has been invalidated, the assumptions and meanings associated with racial distinctions linger on and still exercise a malign influence in many settings.

There is an important parallel here with the distinction between mental and physical illness. The scientific basis for that distinction has also been discredited, but the assumptions associated with it are still influential and damaging. Sykes, whose primary concern is to establish that CFS and other somatoform disorders are physical illnesses, would have us preserve the discredited distinction between physical and mental illnesses in order to achieve that end. Instead of arguing that the distinction must be preserved because it is still meaningful to many people, he would, in my view, do better to accept that it has become deeply misleading and help to hasten its demise. That would surely be in the long-term interests of the patients he is trying to help.

Although the arguments for abandoning the late-eighteenth-century distinction between physical and mental diseases owe little to the assortment of syndromes currently known as somatoform disorders, they illustrate very clearly the near impossibility of distinguishing between physical and mental. DSM–IV (American Psychiatric Association, 1994: p. 445) openly concedes that ‘the grouping of these disorders in a single section is based on clinical utility … rather than on assumptions regarding shared aetiology or mechanism’ and ICD–10 (World Health Organization, 1992: p. 161) observes that ‘the degree of understanding, either physical or psychological, that can be achieved about the cause of the symptoms is often disappointing and frustrating for both patient and doctor’.

Sykes's own attempt to convince us that CFS is a physical illness depends primarily on the bald assertion that it should be assumed to be physical unless there is convincing evidence in the individual patient of ‘psychological causation’. This is despite the fact that if this criterion were to be applied to such prototypical mental disorders as schizophrenia, bipolar disorder and Alzheimer's disease, none would qualify. He then tries to buttress this patently inadequate criterion by asserting that ‘psychological causation should not be imputed in difficult cases where there is no widespread agreement’ and by misrepresenting as an experience of physical illness the belief of many of the patients who regard themselves as suffering from ‘ME’ that their illness is physical. One is left with the strong impression that any argument will do so long as it produces the desired conclusion.