The plausibility of the medical model largely relies on the assumption that the diagnostic indicators of schizophrenia fit into generally accepted notions of what constitutes a disease. But these notions are not stable and they sometimes change with fashion and public debate. Comparisons can be made between schizophrenia and a number of other human conditions where the 'disease' label is also in dispute.
Baldness is a good comparison. Does baldness have an underlying pathological cause requiring medical attention? Is it a natural part of the aging process? Or is it merely a stylistic affectation some people express by shaving their heads?
Homosexuality also provides some interesting parallels. Is it a manifestation of mental disease requiring medical treatment? Is it one of a variety of natural forms of sexual expression? Or is it an adaptation that some people—such as prisoners—choose to make when they are denied the companionship of the opposite sex?
In both cases it should be fairly apparent that the third assumption, that they have non-existent causes and are the result of personal choices, most certainly applies to some people who fall into these two classes, but obviously not to all. But choosing between the other two positions, pathological and natural, is more difficult.
One approach to understanding what is a disease and what is not a disease is to consider how it relates to function. Function is an attractive approach because the arguments can be made to appear objective. If the function of hair on top of a man’s head, for instance, is to provide insulation for his brain against extremes of heat and cold, and the climate demands this insulation so that a bald man must take special precautions, then a lack of hair might be considered a malfunction and therefore a disease.
But if, on the other hand, the function of hair on a man’s head is to attract sexual attention, and the baldness only develops after the man is no longer sexually active, then lack of hair in an elderly man would hardly constitute a malfunction. But some human features have both function and accidental utility and it is important to distinguish between them. A nose, for instance, ‘has the function of heating and humidifying inspired air’ but it also has the accidental utility of being able to support spectacles. So according to this line of thinking, a nose that functions properly, although it is unusually shaped, might be an oddity, but it wouldn’t be diseased simply because it was unsuitable for supporting spectacles.
The function test can also be applied to homosexuality, but there might be philosophical problems to solve in choosing between possible functions. Is the function of human sexuality to procreate, or is it to give pleasure? If it is to procreate, then homosexual expression might be considered a malfunction. But such an argument would also render all other non-reproductive sexual expression, involving contraception and bad timing, a malfunction, and therefore diseased as well.
The test of functionality is even more problematic when it is applied to schizophrenia. One of the functions of the human mind is the formulation of thoughts and beliefs. But the mere formulation of thoughts that appear to normal people to be unusual or bizarre, and beliefs (delusions) that are judged to be false, is not enough in itself to indicate malfunction. A mind could only malfunction in this regard if it had first been clearly established that functional thoughts and beliefs must necessarily conform with social norms.
A converse problem with the functionality test occurs when it is agreed that a certain condition definitely indicates malfunction but the cause of the malfunction is in dispute. Death, for instance, is a fairly definite indication of serious malfunctioning. Yet surveys of medical students, interns and hospital resident doctors have shown that only 56–57 per cent of them can correctly identify causes of death on death certificates. This converse approach to malfunction can be tested on a schizophrenic symptom such as hallucinations. It might be agreed that an hallucinating mind is definitely malfunctioning, but theories on the cause of the hallucinations might range from something essentially non-medical such as fatigue to a cause that is indisputably medical such as malarial infection.
If the functionality test for distinguishing disease is problematic there are several other tests to try. One involves discarding the pseudo-objectivity of functionality by adopting normativism, which defines diseases in terms of harm. On the surface this is a simple premise: if a person is harmed in any way by having a certain condition, and is worse off than they would otherwise be, then the condition can be described as a disease.
Many non-controversial disease descriptions, such as cancer and cholera, are easily accommodated by the test of ‘harm’. But problems are soon encountered when the test of ‘harm’ is applied more widely. On the one hand there are many conditions which apparently cause harm, such as ignorance and clumsiness, but which are not usually described as diseases. While on the other hand, a mild dose of what is clearly understood as a disease, in the form of a vaccination, for instance, can be good for a person, rather than harmful.
The problem with using ‘harm’ as the criterion for determining disease is further exacerbated if we return to our three test cases: baldness, homosexuality and schizophrenia. In each case there are circumstances in which a major aspect of the harm that can be caused by these conditions appears to come from cultural values, in the forms of aesthetics, prejudice and discrimination, rather than from individual incapacity. If we were to allow social harm to determine what is and is not disease we might leave the door open to claims that beautiful people are more healthy than ugly people; that light coloured skin in a predominantly black society, and vice versa, are diseases; and that personal traits that tend to give offence, such as vulgarity, loud voices and excitable behaviour, are all symptoms of disease.
A further problem with the concept of ‘harm’ is that from time to time medical scientists develop notions that certain conditions are harmful, and forcefully propagate their view. Subsequently, however, a consensus view might develop that relegates this condition back to the status of non-disease. There are a number of examples of this tendency, the more notable ones often being to do with reproductive organs. In 1856, for instance, ‘T. B. Curling considered that the frequent emission of sperm gave rise to "constitutional symptoms of a serious character", and constituted the disease of "spermatorrhoea" . . . However, frequent ejaculation is not harmful, and so there is no such disease.’
Another approach to the nature of disease would be to consider the question of whether diseases are invented or discovered. To argue that diseases are discovered is to assume that disease classification is an ongoing process after the fashion of biological and botanical classification systems. But there is a major problem with this assumption. Diseases derive their class identity from human values and human attitudes towards them. Two bacteria might share very similar properties and be both placed in the same biological family, but only the one that causes human disapproval, through causing ill-health in humans, or to domesticated animals or food crops, will be classified as a disease-causing organism. When looked at this way it seems apparent that human values play an essential part in the 'discovery' of any disease.
That leaves the question of whether diseases are invented. Most diseases have sufficient evidence to satisfy one or another of the notions of disease and plausibly demonstrate that they are not inventions of the medical profession. But some, like the disease of "spermatorrhoea", look very much as if they might have been invented. To psychiatric sceptics, schizophrenia looks like one of these. These doubts about the validity of schizophrenia are continually fed by news reports like a recent one from the annual conference of the Royal College of Psychiatrists. Delegates were told about research which found that British psychiatrists are strongly influenced in their diagnoses by the Christian names of their patients. A survey of British psychiatrists found they are more attracted to the name Matthew than to Wayne. As a consequence of this name preference patients named "Matthew received a diagnosis of schizophrenia significantly more frequently than Wayne (77% vs. 57%)".
Unless medical researchers can find an underlying cause to show there is more to schizophrenia than just a psychiatric imperative to treat the symptoms, schizophrenia's disease status will always be questioned. Unfortunately for the psychiatric profession, however, despite the concentration of money and energy that is directed into this quest, the results so far have been very poor.
 Jenny J. van Drimmelen-Krabbe et al., ‘Homosexuality in the International Classification of Diseases: a clarification’, p. 1660.
 Lawrie Reznek, The Nature of Disease, p. 98.
 Ibid., p. 100.
 Jacqueline Messite and Steven D. Stellman, ‘Accuracy of death certificate completion: the need for formalized physician training’, pp. 794–7.
 Reznek, op. cit., p. 208.
 Royal College of Psychiatrists, 'Stereotypical attitudes towards Christian names and gender may influence diagnosis'.