What did Canada's Supreme Court and the Clarity Act say about a province leaving?

In 1998 Canada's Supreme Court said that a province cannot leave on its own, and that a clear vote to leave would still have to lead to negotiations. The Court concluded that Quebec could not secede unilaterally under Canadian or international law. However, the Government of Canada would have to negotiate with the Quebec government if Quebecers expressed a clear will to secede.

The case began after Quebec's 1995 referendum came close. Lucien Bouchard, then Quebec's premier, said he would hold another referendum when the "winning conditions" were there. In reaction, Prime Minister Jean Chrétien asked the Supreme Court about the legality of a unilateral declaration of independence by a province. The Quebec government refused to take part, so the Court appointed an amicus curiae, André Jolicoeur, to present the argument Quebec might have made.

The Court said that a vote, by however strong a majority, would have no legal effect on its own. It could not push aside federalism, the rule of law, the rights of individuals and minorities, or the operation of democracy in the rest of Canada. But it also said that if Quebecers expressed a clear will to secede, the Government of Canada would have to negotiate, and the rest of Canada would have no basis to deny the Quebec government the right to pursue secession.

In 2000 Parliament passed the Clarity Act, based on the ruling. It lets the House of Commons decide whether a referendum question is clear before the vote, and whether a clear majority has spoken after it. The Court did not define a clear majority, and the Act sets no numerical threshold, so those judgments are left to politicians. Both the Quebec government and the Government of Canada said they were pleased with the Court's opinion.