In December of 2013, 13-year-old Jahi McMath was declared “brain dead” by doctors at Children’s Hospital in Oakland, California, in accordance with California law. When pronounced dead, she was still breathing on a ventilator and her heart was still pumping blood. Her mother to this day insists that the doctors’ tests were wrong, and that Jahi is still alive. As of this writing, her heart continues to beat and the courts have not determined definitively whether she is dead or alive. The courts are expected to resolve the matter soon.

There was a time when everyone more or less knew what death meant. It was signaled by the stopping of the heart, the ending of blood flow, and ceasing of respiration. The stoppage had to be irreversible (an idea that is more complicated than it may appear), but once blood and breath were gone forever, that signaled the end of a person’s existence. In the last fifty or so years, however, all that has changed. It is fair to say in some ways we know less today about what it means to die than we ever have. At the same time, we know more about how complicated it is to determine that someone has died.

Beginning in the 1970s some began to question whether the irreversible stoppage of circulatory and respiratory systems is a signal of death or is that stoppage merely an indirect sign that some other event has occurred in the body, like the irreversible cessation of the integration of bodily functions so that the body no longer functions as a whole. Even if some individual parts (such as a kidney or a liver) could function, death was beginning to be described as the irreversible cessation of integrated bodily function. The stoppage of the circulatory and respiratory systems, rather than being intrinsically definitive as the meaning of death, could be thought of as a signal of something more basic and systemic happening in the body such as the loss of the body’s capacity to integrate its functions, a capacity many assume is seated in the brain.

About this same time, roughly the middle of the last century, medical technology was developing rapidly. Cardiopulmonary respiration (CPR), heart-lung machines, and similar technologies permitted not only mechanical breathing for patients, but also mechanical circulation of the blood. We began to realize that bodies could theoretically be maintained indefinitely even after heart and lungs could no longer function spontaneously.

In 1959, two French neurophysiologists, Pierre Mollaret and Maurice Goulon, described respirator-dependent patients in extremely deep coma, and called the condition coma dépassé. The patients lacked electrophysiological activity and reflexes. Soon the question was asked whether these patients, who lacked the bodily integrating capacity controlled by the brain, should be considered “dead” even though breath flowed using mechanical ventilation and therefore the heart continued to beat.

In 1968, a committee called the “Ad Hoc Committee of the Harvard Medical School to Examine the Definition of Brain Death” published a report in the Journal of the American Medical Association claiming to identify the criteria that would establish the death of the brain. Although they did not explicitly argue the claim, they implied that people who meet their criteria for the death of the brain should be treated as deceased—as dead people. While some people took this as a mere refinement in the way of identifying death defined as loss of integrating capacity of the body in cases in which ventilation and circulation are maintained mechanically and thus mask the body’s loss of integrating capacity, others were referring to this as a new definition of death, that is, the abandonment of the belief that circulation and respiration loss were intrinsically important in classifying a person as dead.

By 1970 Kansas had passed a law authorizing death pronouncement based on either neurological criteria or circulatory criteria. Other states soon followed. By 1981 a President’s Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research had refined the arguments and endorsed the view that people should be considered dead if they had irreversibly lost all functions of the brain. A group of consultants to that group formulated a revised set of criteria for measuring the death of the brain.

Despite these official declarations, scholars began to realize that perhaps not all of the functions of brain had to be lost in order to lose the critical capacities of an individual necessary for being considered alive. A 1971 paper by J. B. Brierley and his colleagues described two patients who had lost very important brain functions including all cerebral functions but had retained some functions centered in the brain stem such as reflexes and respiratory center control. These patients were permanently unconscious, but could breathe on their own. Based on such observations, some proposed an even more avant-garde definition of death whereby people could be classified as dead if they had irreversibly lost consciousness and other brain functions located above the brain stem. This came to be called the “higher-brain” definition of death.

The result was that by the end of the century there were three competing groups of definitions of death: one based on circulatory function loss, a second based on loss of all brain functions, and a third based on loss of higher functions like consciousness. In fact, each of these has many sub-variants depending on whether it is the anatomical structure that is lost or merely the physiological function; whether the continued living of individual cells counted as life or only the clusters of cells needed to perform certain functions, and, in the case of higher-brain death, exactly which functions were considered “higher.”

In our new book, Defining Death: The Case for Choice, we confront the persistent disagreement about what it means to be dead. Relying on the claim that the choice of a definition is essentially a religious or philosophical one rather than one based on science, we propose that each legal jurisdiction adopt one of the three major alternative definitions, but permit people who conscientiously prefer one of the others to have the alternative definition used for their own death pronouncement. For the majority who do not actively choose a definition, we suggest that states adopt, as a default, the definition based on loss of all brain functions (noting that usually loss of brain functions can be measured either directly based on neurological tests or indirectly based on loss of circulation). Although some may worry that this would produce chaos in hospitals and in insurance plans, we show otherwise, and conclude that the only defensible option might be to give people a choice among reasonable alternatives for the definition of death.