The machine metaphor in medicine

Further cogitations on health

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In the first part of a paper I will present at the Austrian Economics Research Conference next week, I talk about the healthcare system’s elephant in the room: how an activity that occupies 18 percent of GDP is doing so without any precise definition of health.

The lack of definition does not mean that there aren’t any prevailing notions about health.  In fact, there is one particular concept that is clearly dominant, however implicit or covert it may be: it’s the notion of health that emerges if one adopts the “machine metaphor” for the body, a metaphor that is as pervasive as could be, given that it seems to have no viable counterpart (see, for example, here).

The machine metaphor was famously proposed by René Descartes in the first half of the seventeeth century.  He conceived of the universe as comprising three substances: res extensa (measurable things), res cogitans (thinking things), and God.  Animals are automatons.  Human bodies are like those of animals, but connected to a thinking thing (soul) by way of the pineal gland.  A healthy body is like a “well-made clock.”

In a sense, Descartes’ postulate was prescient.  Over the next two hundred years, as empirical science (the study of measurable things) began to bear astonishing fruit, the machine metaphor became almost essential for our conception of organisms, including human beings.  And, with the development of psychiatry, neurology, psychology, and neuroscience, the res cogitans looked like it would soon be folded into the res extensa.  However strongly or weakly one believes in the machine model, it remains an important presupposition in the biological sciences.

I will not go into the merits or demerits of the machine metaphor here, but wish simply to point out the difficulty that it causes in regards to the notion of health.

Since a machine is an assemblage of parts functioning in concert to achieve particular ends, the metaphor of the machine implies that diseases are dysfunctions of the body, and that health is the absence of disease.  In fact, that is the typical definition of health found in medical dictionaries.

My car is “healthy” if and only if its parts are healthy and work well together.  A gasket, a piston, or an axle can be examined separately, and the defect in the function of the car can be traced down to a defect in the part.  And my car can be deemed unhealthy by an objective observer even if it performs the bare minimum job that I care about, which is take me to and from work.

But that understanding of health—that the health of the whole depends on the health of the parts—does not seem to correspond to the way people naturally employ the term for themselves.

According to the machine metaphor, a blind person or an amputee could never be considered healthy: the eye or the leg are clearly defective.  Yet I’m sure there are many blind persons and many amputees who emphatically claim to be perfectly well.  Likewise, I have met many elderly people who have assured me that they are in excellent health, regardless of how many infirmities and disabilities they are able to identify in themselves.

The question then becomes: is the aim of medicine to treat and fend off externally identified diseases or to maintain and restore a personal conception of health?

Of course, many other concepts of health exist to take into account its subjectivity.  Not least among them is the WHO definition of health as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.  But even if we take the silly word “complete” out of the definition, does this version adequately capture our common sense notion about health?

Equating well-being with health may force us to pay attention to the patient’s experience, and not merely “inspect the machine,” but I don’t think that the emphasis on feelings is necessarily the correct one.  The WHO definition, too, appeals to philosophical empiricism: the res extensa is acknowledged to be res sentiens, but that still comes short of capturing the whole of human reality.

I’ll have more to say about this when I return from Auburn but, in the meantime, I encourage you to read the work of Daniel Nicholson, a young faculty at the University of Exeter who has written extensively about the machine concept of the organism and its historical development.  If you’re interested in this topic, you may also want to read a draft paper of mine about the definition of health proposed by Christopher Boorse.  In the first part, I sketch the evolution of the ideas of health in Western medicine.  Boorse claims to have come up with a definition of health that is entirely value-free or, as he put, “as value-laden as organic chemistry or astrophysics.

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