How should we define the death of a person? Philosophers and physicians have long pondered this question, yet we still don’t have a satisfactory answer. For much of human history, death was synonymous with the cessation of the heartbeat. However, there are patients in hospitals whose hearts are still beating but who appear to be less than fully alive. Are they dead?

Fifty years ago, a Harvard committee tried to bring a modern perspective to this question. The chairman, Henry Beecher, a renowned bioethicist, was motivated by the conundrum of “hopelessly unconscious” patients being kept alive by mechanical ventilation and other newly developed medical technologies. Such patients were “increasing in numbers over the land,” he wrote.

Dr. Beecher’s committee, in a report titled “A Definition of Irreversible Coma,” defined a new state of death — brain death — in which patients were unconscious, unresponsive to pain and unable to breathe on their own, and had no basic reflexes (pupils unreactive to light, no gag reflex and so on). These were conditions suggesting a brain stem that was irreversibly damaged. Such patients, the committee asserted, were in fact dead and could be declared so by a physician. Additional tests, such as a flat brain-wave scan or an angiogram showing no cerebral blood flow, could be used to confirm the diagnosis but were not necessary.

The Harvard committee’s concept of brain death was eventually accepted by states across the country. Today, patients in the United States and many other countries can be declared dead either because their hearts have stopped or because their brains have ceased to function, even if blood is still circulating.

In the years after the Harvard report was published, doctors relied on the concept of brain death to withdraw life support from neurologically devastated patients, curtailing futile care. Just as important, brain-dead patients were declared deceased before their blood had stopped circulating, thus minimizing injury to other vital organs, allowing them to be transplanted. Some physicians believe that facilitating organ transplantation was the Harvard committee’s true aim in redefining death.

“There is great need for the tissues and organs of the hopelessly comatose in order to restore to health those who are still salvageable,” the committee wrote in an early draft of its report — though this sentence did not appear in the final version. In the years just before the report’s publication, doctors had performed the first liver, lung and heart transplants. The number of available organs, then as now, was small, however, and there was a great desire to expand the pool.

In the main, this goal was achieved. After the Harvard committee issued its report, the number of transplanted organs drastically increased, and thousands of patients waiting on organ transplant lists were saved. Today, brain-dead individuals supply most of the transplanted organs in the United States. Because of the opioid epidemic, those numbers have increased. Deaths from opioid overdose now account for about 13 percent of the nation’s organ donors, up from 1 percent two decades ago.

But the concept of brain death was controversial from the start. Many people, including many Native Americans, evangelical Protestants and Orthodox Jews, rejected the concept of brain death for religious or cultural reasons. Even apart from such considerations, a determination of brain death can seem implausible in the face of a healthy body: Some patients who have been declared brain-dead whose life support has not been withdrawn have “survived” with intact organ function for months, even years. These patients often don’t look “dead.” They may have warm skin and a normal complexion and may continue to grow, menstruate, even gestate children. Families still come up to me in the intensive care unit and say: “His heart is beating, Doctor. How can he be dead?”

Because of improvements in technology, organs designated for transplantation today can be nourished and remain viable for longer periods, so it is less critical to remove organs before the heart stops beating. As a result, more organs, especially in Europe, are being removed and transplanted after the more traditional declaration of death: the stoppage of blood circulation. Death in these cases is declared the old-fashioned way, after the heart stops beating, typically after withdrawal of life support. As technology continues to advance, we may even be able to return to the original definition of death, should we want to.

All of which serves as a reminder that our definition of death is man-made. In the spectrum between alive and dead, we set the threshold, and we can do so in response to biological, ethical and even practical considerations. Death is not a binary state or a simple biological fact but a complex social choice.