Quebec's distinctive character must be reflected in the appointment of judges to the Supreme Court of Canada, and nothing short of unanimous agreement of the provinces can change that principle, the country's highest court has ruled.

It was a stunning rejection of Prime Minister Stephen Harper's latest appointment to that court, Justice Marc Nadon, who was ruled ineligible for the court because he did not have current Quebec qualifications, either on a superior court or as a lawyer with current standing in that province. The Conservative government had tried to change the law to make Justice Nadon eligible, but the court said there is a special appointment process for the Supreme Court's three Quebec judges that is protected by the Canadian Constitution from such unilateral changes.

The ruling leaves Mr. Harper to go back to the same pool of candidates he rejected when he plucked the obscure, semi-retired judge from the Federal Court of Appeal in late September.

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The 6-1 ruling was not offered as the work of one judge but instead signed by the six judges in the majority. This shared authorship often occurs in national-unity cases, to give the impression the court is speaking with one voice (or in this case, one voice plus a dissenter).

In theory, Mr. Harper could decide that Justice Nadon deserves a chance to qualify for admission to the Quebec bar, or be placed for a day on a senior Quebec court, which would put the 64-year-old in place to be appointed again. But those back doors to the country's highest court would be such a slap at Quebec, and at the reasoning behind the Supreme Court ruling, that it could create a constitutional and political crisis, legal observers say. And it would almost certainly be one more round of severe unpleasantness for Justice Nadon, who was not commenting on Friday.

The Prime Minister's Office suggested it has not even begun to think about what to do, issuing a statement saying it is "genuinely surprised" by the ruling and considering its options.

So where to, next? Two of the most widely respected judges in Quebec, Justices Marie-France Bich and Nicholas Kasirer of the Quebec Court of Appeal, are both former academics whose cerebral and sometimes innovative approach was what Mr. Harper passed over in September. The Harper government has, however, looked favourably on Justice Kasirer in the past, appointing him to the appeal court in 2009 from his job as dean of law at McGill University.

"Is Harper going to be welcoming to those kinds of characters? Probably not so much," University of Toronto law professor David Schneiderman said in an interview.

But the challenge, he said, is to find conservative, deferential judges who will tend to shy away from bold decisions expanding the rights in the Charter of Rights and Freedoms. "It's not like there's a deep pool of like-minded Harperites," he said.

Daniel Turp, a law professor at the University of Montreal, said the botched appointment is a lesson in what happens when a prime minister prefers deference to merit. "What I heard from many of my colleagues in the legal community, judges included, although they don't want to be on the record – they thought the appointment [of Justice Nadon] was totally unacceptable."

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And so there are still eight judges on the Supreme Court of Canada. And just two from Quebec. The court has been short-handed for nearly seven full months. It has never been so short for so long in the post-1982 era of the Charter of Rights and Freedoms – an era that began with more than one stress burnout of a Supreme Court judge.

But the court's credibility has not suffered, legal observers say. Far from it, they say. It was enhanced by a historic ruling that will take its place alongside the 1998 secession ruling on what it would take to break up Canada. It was a history lesson on the compromise between French and English that is Canada: "The eligibility requirements for appointments from Quebec are the result of the historic bargain that gave birth to the Court in 1875." Section 6 of the Supreme Court Act, whose interpretation was at stake in the case, "protects both the functioning and the legitimacy of the Supreme Court as a general court of appeal for Canada."

Paul Daly, who teaches administrative law at the University of Montreal, called the ruling "a huge day for the Canadian federation. This is a ringing declaration from the Supreme Court of Canada on the importance of Quebec's distinct character and how important it is to protect it."