Update: The Supreme Court has struck down a ban on doctor-assisted suicide. Read the full story.

On Friday, the Supreme Court will rule on whether individuals who are suffering unbearably have a constitutional right to control their own death. The ruling comes 22 years after the court narrowly rejected the claim of 42-year-old Sue Rodriguez, dying of amyotrophic lateral sclerosis (ALS), to a right to a physician's help in ending her life. The 5-4 ruling said the state's purpose in banning assisted suicide was legitimate – to protect the sanctity of life. Here are 10 things to know about the current case, called Lee Carter, et al. v. Attorney General of Canada, et al.

1. Why it is one of the biggest Supreme Court rulings in history: It could change the way Canadians are permitted by their government to die. "It affects every single Canadian. It affects your life, my life and the life of our friends and family who may be or are terminally ill," Chris Considine, a Victoria lawyer who represented Ms. Rodriguez, said in an interview. In its effect on Canadians' basic choices over life and death, it could rank with the Supreme Court's 1988 ruling striking down the abortion law.

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2. Who brought the case: Kathleen Carter, 89, suffered from the painful degenerative condition spinal stenosis. She said in an affidavit she did not wish to live "as an ironing board," flat on her back, unable even to read a newspaper. Her daughter Lee took her to Switzerland in 2010 for an assisted death. Gloria Taylor, 64, like Ms. Rodriguez, suffered from ALS, which made her fear she would "eventually suffocate and die struggling for air, like a fish out of water," she said in an affidavit. She died of an infection in late 2012.

3. What the law says: "Everyone who (a) counsels a person to commit suicide, or (b) aids or abets a person to commit suicide, whether suicide ensues or not, is guilty of an indictable offence and liable to imprisonment for a term not exceeding fourteen years."

4. What the federal Attorney-General argued: "An absolute prohibition sends the message that all lives are valued, and worthy of protection from those who may subtly encourage vulnerable people to terminate their lives."

5. Why the trial judge rejected the slippery-slope argument: Jurisdictions that have adopted physician-assisted death since the 1993 Supreme Court majority include Luxembourg, Belgium, the Netherlands, Washington State and Oregon. In all those, risks to the vulnerable are "substantially minimized," Justice Lynn Smith of the B.C. Supreme Court found when she struck down the law in 2012. She also found that laws banning assisted dying prolong suffering and cause some people to take their lives sooner than they would otherwise, while they are still able to.

6. Why the trial judge's factual findings may prove pivotal: The Supreme Court ruled 14 months ago in striking down federal laws on prostitution that appeal-court judges must defer to trial judges' findings of "social and legislative facts." In that case, a trial judge said the effect of prostitution laws is to create potentially deadly dangers for vulnerable people. Framed that way, the Supreme Court said it could only conclude government has no right to pass laws that could lead to people being killed. In the assisted-suicide case, "the government is trying to justify an absolute prohibition that has a serious impact on personal autonomy and causes enormous individual suffering," University of Ottawa law professor Carissima Mathen says. "The trial judge found that the evidence just didn't support the need for that absolute prohibition. The other reason that the factual findings are especially important here is that they paint such a stark picture of the suffering of those who are physically incapacitated but cannot choose the timing of their own death."

7. Key exchange at the Supreme Court hearing: Federal lawyer Robert Frater argued that Justice Smith went beyond her rightful role and did a job that belongs to government in examining how laws in other jurisdictions helped vulnerable, suffering people. Justice Marshall Rothstein, who tends to be one of the court's more conservative members, said that Justice Smith "was just looking at the evidence and that's what the evidence caused her to conclude. What's legislative about that?"

8. Should such life-and-death matters be decided by unelected judges or Parliament? In 1993, the Supreme Court wasn't ready to trod on Parliament's toes in this area, some legal observers say. The Charter was too new, and so was the debate over assisted suicide. "It was only 11 years after the Charter and there was a reluctance," University of Montreal law professor Michel Morin says. But today, says University of Calgary law dean Ian Holloway, "it seems to me we've decided to leave all the hard questions to the courts."

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9. Cases in which the court has rejected its previous rulings: Just last week, the court declared a constitutional right to strike, rejecting its own 1987 ruling on the principle; a week before, it said Mounties have a right to unionize, expressly rejecting a 1990 ruling on Mounties unionizing. Other examples include Burns and Rafay (2001), in which the court overturned a 1991 ruling and refused to allow extradition to face a possible death penalty, and Brooks, a 1989 ruling in which the court banned discrimination against pregnant women, overturning a pre-Charter ruling.

10. Timing: The court, with a majority of its members appointed by Prime Minister Stephen Harper, has headed boldly out in new directions repeatedly in the past year, with far-reaching rulings on labour rights, aboriginal rights and the rights of sex-trade workers, and rulings rejecting or softening Conservative attempts to toughen the treatment of prisoners.