Health is not a “state of complete physical, mental, and social well-being”. And nor is it “merely the absence of disease or infirmity”. The first part of this formulation is enshrined in WHO’s famous founding constitution, adopted in 1946. It was supposed to provide a transformative vision of “health for all”, one that went beyond the prevailing negative conception of health based on an “absence” of pathology. But neither definition will do in an era marked by new understandings of disease at molecular, individual, and societal levels. Given that we now know the important influence of the genome in disease, even the most optimistic health advocate surely has to accept the impossibility of risk-free wellbeing.

That said, the conjunction of the physical, psychological, and social remains powerfully relevant to this day. Indeed, this framework should be extended in two further dimensions. First, human health cannot be separated from the health of our total planetary biodiversity. Human beings do not exist in a biological vacuum. We live in an interdependent existence with the totality of the living world. The second dimension is in the realm of the inanimate. The living world depends upon a healthy interaction with the inanimate world. Thanks to the science of climate change, we now understand only too well how contingent our human wellbeing is on the “health” of the Earth’s systems of energy exchange.

Science has contributed to our understanding of wellbeing through an ingenious apparatus of techniques that reveal not only the causal pathways of ill health but also evidence for their amelioration. But the language of science can be inhibitory. For example, the notion of suffering is no longer fashionable. It is not a scientific word; it seems vague and old-fashioned, harking back to a time of clinical impotence, when patients had to endure and tolerate pain without respite or relief. Science aims to deliver the means to eliminate much of what once passed for human suffering.

But as the opening article in our Series on health in the occupied Palestinian territory shows, dimensions of suffering, especially at the community level, are measurable and often severe. Science has not eradicated suffering, despite its enormous power to deliver technologies to improve health. Being more humble about the experience of individuals, rather than simply drawing up reductive report cards of their health status, opens up the possibility for a more realistic understanding of what it means to be healthy. The fact is that one cannot be healthy in an unhealthy society.

Health certainly has to encompass these complex determinants of illness. But to say this can induce a feeling of fatigue, even defeat. The obstacles to a minimum quantity of health seem so huge and so complex that it is almost impossible for a single doctor to have any influence on their effects. But if we take a more modest view of what health means, perhaps we may be able to transcend the complexities of disease and offer a very practical mission for modern medicine.

That mission was set out most clearly by a French physician, Georges Canguilhem, in his 1943 book, The Normal and the Pathological. Canguilhem rejected the idea that there were normal or abnormal states of health. He saw health not as something defined statistically or mechanistically. Rather, he saw health as the ability to adapt to one’s environment. Health is not a fixed entity. It varies for every individual, depending on their circumstances. Health is defined not by the doctor, but by the person, according to his or her functional needs. The role of the doctor is to help the individual adapt to their unique prevailing conditions. This should be the meaning of “personalised medicine”.

The beauty of Canguilhem’s definition of health—of normality—is that it includes the animate and inanimate environment, as well as the physical, mental, and social dimensions of human life. It puts the individual patient, not the doctor, in a position of self-determining authority to define his or her health needs. The doctor becomes a partner in delivering those needs.

For a scientific journal too, Canguilhem’s definition is liberating. By using adaptability as the test of health, a journal can evolve to address the changing circumstances of disease. Adaptability frees us to be agile in the face of shifting forces that shape the wellbeing of individuals and populations. Canguilhem’s definition also allows us to respond to disease globally, taking account of the context of conditions in a particular place, as well as time.

Health is an elusive as well as a motivating idea. By replacing perfection with adaptation, we get closer to a more compassionate, comforting, and creative programme for medicine—one to which we can all contribute.