There are two main strands in discussions of disease. I shall call them the biological and the sociological. In terms of the biological strand, 'disease' is a scientific, descriptive term and diseases are discovered and classified by various biological sciences, such as biochemistry, physiology, and public health medicine. The origin of this approach to disease can be found in the ancient Greeks. For example, the biologist-philosopher Aristotle sees the task of the biologist as that of discovering the repeatable features of nature and then of classifying the phenomena in terms of genera and species. In a word, biological science is taxonomy.
This way of thinking enters the early modern world through the 17th-century physician Thomas Sydenham (1624-89) and the 18th-century botanist Carl Linnaeus (1707-78). These influential biologists believed that it was possible to classify, not only plants and animals, but also diseases, into genera and species. According to this approach, types of disease can be discovered and they exist independently of human interests. They would be identified in terms of various malformations, irregular growths, genetic irregularities and so on, which lead to the malfunctioning of an organ or a bodily system. In terms of this type of definition, diseases exist as independent entities and can be studied independently in laboratories.
Such a view is very plausible in general outline and is still very much alive. It has been given new strength by the popular belief that there is a 'gene for' many human ailments, or that ailments are caused by identifiable viruses. Nonetheless, the biological view has limitations which emerge when we examine the second approach to defining disease – the sociological.
The sociological view has a negative and a positive side. Negatively, it finds a range of problems in the biological view. Its exponents point out that there are some phenomena which are regarded as diseases by some social groups but not by others. Examples are a range of conditions associated with ageing, such as failing vision or hearing, stiffness in the joints or, controversially, dementia in the elderly. The sociological approach would suggest that value judgements and cultural norms are the factors which determine whether these are diseases or not. From the biological standpoint, they are statistically normal.
More positively, the sociological approach invites us to see disease in terms of the impairment of human function taken as a whole. In the biological approach, disease is associated with failings in organs or parts of the body, but in the sociological it is thought to apply to the whole human organism. From the sociological perspective, human beings are diseased if they cannot function normally, where 'normal' is interpreted in terms of the norms of a given culture. 'Disease' ('illness' or 'disability'), they say, characterise a life as a whole, as it is acted out in a given society, and the terms apply only derivatively to an organ or part of the body. The stress in the sociological approach, then, is on the evaluative nature of the concept of disease, and the values of a given culture. For example, in some cultures obesity might be ranked as a disease but in others it might be seen as a sign of affluence or status.
Diseases, for the sociological way of thinking, are not discovered, and they have no timeless, absolute definition. Rather, they are defined by the changing values, norms, and social expectations of a given society. To some extent, diseases and their treatments are matters of cultural expectation. This is clear in the case of mental illness. Young people brought up in the 1930s or during the Second World War faced severe and stressful threats to their livelihoods and indeed their lives. But they did not claim to be mentally ill. In our contemporary culture, the situation is very different.
Nonetheless, there are also real problems with the sociological line. I shall mention two difficulties. First, science can identify particular, anatomically-located diseases. These are attributable to specific organs or systems, and not to the person as a whole. For example, someone might have diseased lungs and be dying in a palliative care unit, but overall, as a person, he/she might experience the wellbeing of someone who has made peace with friends and family and is ready to go. So a diseased bodily part can exist alongside overall wellbeing.
Second, there is general agreement in the medical sciences about what biochemical or physiological states should be viewed as healthy and what viewed as diseased. It is true that, in many cases, there might be dispute at the margins. For example, there might be dispute as to whether a given cholesterol level is too high. But, nevertheless, there is agreement that certain levels indicate disease and others are entirely normal. This seems to suggest that disease language is at least mainly scientific, and a non-evaluative definition would therefore be appropriate.
We seem to have reached an impasse. The biological and the sociological approaches are plausible in their criticisms of each other, but neither has a fully persuasive positive theory. The solution might be to look for a new approach.
A new approach might be to drop the whole idea of defining 'disease' and substitute the idea of 'clinical problem'. In developing this line, we might say that language can misguide, and concepts by their very character can misdirect us. Disease-concepts have been distorted on the one hand by the assumption that they name things in the world in a value-free fashion, and on the other hand by the assumption that they are purely human value-constructs. The new suggestion is that we should simply bypass questions of definition and see disease-concepts instead as goal-directed notions.
What are the goals? It might be claimed that they are the goals of medicine. These we might characterise in general terms as the attempt to prolong life, where that is worthwhile; to free us from pain; and to minimise impairments to everyday function. Certain physiological and anatomical states are likely to impede the achievement of these important human goals in any environment. Obvious examples are the major cancers and heart diseases. They will therefore constitute cross-culturally recognisable diseases. However, other states of affairs, such as the failings of age, will count as diseases in some societies but not in others.
Looking at the situation more broadly, we might say that it is an error to try to define the nature of disease. Different sorts of answer may be appropriate for evolutionary biology and for clinical medicine. The concern of doctors and patients is with clinical problems. Now, if clinical medicine is focused on resolving clinical problems connected with prolonging life, minimising pain, and improving impaired everyday functioning, then it will allow with equal propriety as clinical problems: lung cancer, schizophrenia, the pains of childbirth, mental health problems, and unwanted sterility, as well as difficulties like stiff joints. That list contains some problems which are classic diseases, others which are conceptually borderline, and others which don't fall under the heading of 'disease' at all.
The point is that clinical medicine is interested in reliable warrants for useful medical interventions, and the question whether something is or is not a disease then becomes irrelevant. As a warrant for medical intervention, I suggest that clinical judgement and the patient's consent are more reliable guides than biological disease-taxonomies or definitions.
This approach has certain merits for both patients and clinical medicine in that it side-steps the philosophical problem of definition. But the 'clinical judgement' approach throws open medicine to inputs from wider non-medical community agencies.
The British Medical Journal
once ran an issue on 'non-diseases'. The editor listed the top 20 non-diseases, which included boredom, baldness, freckles, jet lag, unhappiness and road rage. From a narrowly medical point of view, a merit of the disease-entity approach is that it can stop clinical medicine being forced to take over all the ills of life. The clinician can say: where there is no underlying pathological condition there is nothing for clinical medicine. Yes, but from the patient's perspective there may still be a need for help or advice, and this where wider community services have a role.
Robin Downie is Emeritus Professor of Moral Philosophy at the University of Glasgow