It's not always easy to determine if someone is dead. Science, medicine, law or religions don't always offer simple guidance either.

But specific details around death do matter, and are not merely topics for philosophical debate. For example, when should someone be taken off life support? When is someone dead enough for organ donation? 

The difficult topic of death will be at the forefront in Ottawa this week as the Supreme Court of Canada hears arguments in a case that could make medically assisted death legal on a federal level.

That court action is hardly the only legal focus on medical and ethical questions that can arise around death. 

Last week, lawyers were in court in California arguing over whether 13-year-old Jahi McMath is dead or not. After surgery went wrong in December, her doctors declared her brain dead.

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Jahi McMath's family is asking a California court to reverse the declaration of death in her case. (File/Courtesy of McMath family/Associated Press)

They wanted to take her off life support but her grieving family objected and went to court. Even though there's a death certificate for McMath, the family wants the court to reverse the declaration of death.

Neurologists have recently provided evidence for both sides.

Dr. Paul Fisher, head of Stanford Hospital's division of child neurology, argues she's dead.

Dr. Alan Shewmon, professor emeritus in neurology at UCLA, argues "she is an extremely disabled but very much alive teenage girl."

The McMath case and others raise longstanding questions about death for which the answers are evolving.

When is someone dead?

"I know when one is dead, and when one lives," King Lear declared in William Shakespeare's play.

Lear thought it depended on whether someone was breathing: "Lend me a looking-glass; if that her breath will mist or stain the stone, why, then she lives," he says about his late daughter, Cordelia.

But then, in grief, Lear wasn't so certain.

However, not breathing was then a common way to determine when to declare someone dead. In the 17th century, that was determined by when the heart stopped beating.

By the late 19th century, cardiopulmonary resuscitation had revealed the potential flaws in that definition.

"The challenge is that death is a process, and when it’s a process, taking it to one specific time is very difficult," Dr. David Zygun, director of critical care at the University of Alberta, told the CBC's Bob McKeown in the fifth estate documentary, "Dead Enough."

What is brain death?

Defibrillation, ventilation and the intensive care units in hospitals date to the mid-20th century, and together their use called into question the definition of death based on heart function.

Enter the concept of brain death. An early definition is the time when the "irreversible cessation of all that person's brain function occurs," according to the Manitoba legislature in 1975. That was the first statutory definition of death in Canada, according to the Canadian Encyclopedia.

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Defibrillation, ventilation and the ICU together questioned a definition of death based on heart function.

In the second half of the 20th century, brain death increasingly became the legal determinant of death, but it left some experts queasy. Debate continued.

In 2007, the U.S. President's Council on Bioethics issued a white paper, "Controversies in the Determination of Death," that dropped the term "brain death" in favour of "total brain failure."

For the council, death was "cessation of the fundamental vital work of a living organism — the work of self-preservation."

And debate continued.

In an article on brain death in the August 2014 issue of the Journal of Critical Care, American neurologist Michael de Georgia concludes, "the boundary [between life and death] remains shadowy and vague."

The fifth estate documentary first broadcast on CBC-TV on March 21, 2014, tells the story of Shane Becker, who was rushed to Vancouver General Hospital in 2006 with a severe brain injury.

A neurosurgeon determined that "his condition would likely lead to brain death" and "he recommended the withdrawal of life support," according to the hospital.

Becker's mother consented to the donation of his organs.

But then, while holding his hand, she felt a change in her son's grasp. The medical team soon decided to operate. ​Becker recovered, married and is now a father.

When are you dead enough for organ donation?

In 2005, the Canadian Council for Donation and Transplantation revised the national guidelines to make the recommended wait time at least five minutes after the heart stops beating before harvesting organs.

Other countries have longer or shorter wait times. In Italy, it's 20 minutes. In the U.S., transplant teams need to wait just 75 seconds in Denver, two minutes in Pittsburgh.

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The wait times after the heart stops beating before harvesting organs vary from country to country and province to province in Canada.

Saskatchewan, Manitoba and New Brunswick don't even use cardiac death, only brain death.

Once blood circulation stops, internal organs begin to deteriorate rapidly. After two hours, they are usually beyond use.

Dr. Sam Shemie of Montreal Children's Hospital told the fifth estate's McKeown that the 2005 change to the standards "has accounted for over 1,000 transplants in this country that otherwise would never have occurred."

What about near-death experiences?

As difficult as it is to specifically define the moment of death, it is also unclear what people experience at or just before that time.

On the fifth estate, Becker describes what could be called a near-death experience.

"I was floating above my body, looking down on my hospital bed with my limp, lifeless body, and they were weeping, crying, like I had just died in front of them or I was dying in front of them."

He also remembers "an overwhelming sense of frustration."

Becker's account would fit in with what researchers heard during a four-year study of cardiac arrest cases published last week.

About nine per cent of patients in the study reported near-death experiences during resuscitation.

The study's lead author, Dr Sam Parnia, director of resuscitation research at the State University of New York, concluded that "contrary to perception, death is not a specific moment but a potentially reversible process that occurs after any severe illness or accident causes the heart, lungs and brain to cease functioning."

According to the study, "the recalled experience surrounding death now merits further genuine investigation without prejudice."

As Robert Gottlieb writes, while reviewing 17 books about near-death experiences in the current issue of the New York Review of Books, "if their authors are not liars, something happened to these people. But what? Can what they report, however unlikely it sounds, be reconciled with science?"