A young woman lies in a hospital room, hooked up to a ventilator, with her family by her side. They say the girl, Jahi McMath, has entered puberty and sometimes moves on command. Her body remains in good condition. Her heart still beats. Despite these signs we typically associate with life, McMath has been legally dead since 2013.

In January, 25-year-old Justin Smith was caught in the snow and remained in sub-zero temperatures for about 12 hours. When his father found him, he had no pulse, no blood pressure, and wasn’t breathing. He was dead — except he woke up weeks later with all his brain function intact.

Death, in theory, should be clear cut, but its technical and medical definition is anything but. How can the body still function without the brain? And how can we call someone dead if there’s any chance we could resuscitate them later? The 21st century has crushed the idea of death as we always knew it. Thanks to advancements in medicine and technology, we’ve grown uncertain about what death really is — and this uncertainty goes beyond the medical world.

“The fight over what it means to be dead is essentially a philosophical or religious fight,” Robert Veatch, a professor of medical ethics at Georgetown University’s Kennedy Institute of Ethics, told NPR. “In many ways, it’s the abortion question at the other end of life.”

A Definition That Doesn’t Define Much

The simplest definition of death seems definitive: “The end of life.” This is unhelpful once we consider the uncertainty surrounding life — the pro-choice, pro-life debate, and the less politically charged question of  whether a virus can be "alive" demonstrate the problem.

The Uniform Declaration of Death Act in 1980 states two occasions in which an individual may be legally declared dead: “Irreversible cessation of circulatory and respiratory functions; or irreversible cessation of all functions of the entire brain, including the brain stem.”

Though these situations seem clear, several cases that have landed people somewhere between alive and this legal definition of dead have caused uncertainty.

Affairs Of The Heart

The most common form of death occurs when the heart stops, and subsequently, breathing stops. If allowed to continue, this lack of oxygen would irreparably harm the brain, which in turn would cause brain death.

However, many cardiac arrests occur in the hospital, where clinicians can immediately administer CPR or use a defibrillator. If everything goes according to plan, these techniques can reestablish a normal heartbeat — thus, life. Though a person’s heart may have stopped for a few moments, the cessation did not prove irreversible, so the person was not, and is not, legally dead. Rather, the individual was clinically dead, considered the final stage before legal death. The Encyclopedia of Death and Dying explains that clinical death recognizes the presence of “one of the basic criteria for determining death,” yet it does not stand in the way of resuscitation efforts. This term has proven problematic, however, as the idea of a temporary death seems vaguely oxymoronic at best, and a fundamental contradiction at worst.

 The general public and medical professionals both have questioned the amount of time a clinician should persist with CPR attempts. For example, there have been “miracle” cases of people being resuscitated after receiving CPR for more than 45 minutes, though a 2012 study found the median time hospitals spend on CPR after a patient experiences cardiac arrest was 16 to 25 minutes.

This variation in time spent resuscitating and the occurrence of outlier cases raises an uncomfortable question — is a physician letting a person die if they stop CPR too early?

Brain Drain

The second accepted criteria for legal death, concerning the cessation of all brain function, is even more controversial than the first. The brain is more complicated than the heart; it’s an organ that can perform miraculous repairs on itself and adapt to many circumstances. It can be difficult to say when a brain is irreversibly damaged, and even if it is, the rest of the body may be doing an unnervingly good job of keeping up an appearance of life.

Experts say much confusion surrounding brain death stems from a basic misunderstanding. “Many people confuse brain death with coma, vegetative state or other disorders of consciousness,” Dr. James Bernat, director of the clinical ethics program at the Dartmouth-Hitchcock Medical Center, and who serves on the World Health Organization committee on the standards for death determination, told NPR. “In a coma or vegetative state, a person is alive. In both cases, there’s evidence of neurological function — patients can usually breathe on their own, their reflexes might still be intact and they might respond to outside stimuli. In brain death, there is zero brain function.”

Brain stem activity, particularly, may be the most important thing to consider. The most primal part of the brain, the brain stem controls basic functions like breathing, reflexes, and coordination between the brain and spinal cord. Even without any brain function, death remains uncertain.

In the case of 13-year-old Jahi McMath, the girl lost all brain function after surgery complications, and a coroner issued a death certificate. However, her family has won the right to keep their child on a ventilator. On the opposite end of the spectrum, 33-year-old Marlise Munoz was 14 weeks pregnant at the time of her brain death, and kept on a ventilator for two months despite her family’s wishes.

How can one be legally considered dead, yet win the legal right to remain on a ventilator? And in the case of pregnancy and brain death, it seems beyond irrational that a woman can be considered dead while, quite literally, creating life. Situations like McMath’s and Munoz’s have stirred up moral and ethical questions about life support, and how the wishes of the living factor in.

The ethical issues are only one part of the equation, as technological advances have led to more questions rather than answers. Whether its advances in restoring brain function after a person was caught in sub-zero temperatures for hours, or replacing a patient’s blood with saline to stave of their demise, researchers and doctors are creating more and more layers between life and death. As for a solid definition of death? Not likely any time soon, according to Veatch.

“I don’t see any reason why we will ever have unanimous agreement on that question,” he said.