Liberal Leader Michael Ignatieff kicked off his election campaign by ruling out forming a coalition government, if no party wins a majority of seats in Parliament once the ballots are counted on May 2.

Conservative Leader Stephen Harper says the choice is a Conservative majority or a coalition. Adrian Wyld/Canadian PressConservative Leader Stephen Harper's not buying it.

"Let me be perfectly clear: unless Canadians elect a stable national majority government, Michael Ignatieff will form a coalition with the NDP and Bloc Québécois," Harper said moments after announcing the election date.

Ignatieff noted that the party that wins the most seats gets to try to form a government.

"If that is the Liberal Party, then I will be required to rapidly seek the confidence of the newly-elected Parliament," Ignatieff said in a statement released before the election writ was dropped. "If our government cannot win the support of the House, then Mr. Harper will be called on to form a government and face the same challenge. That is our constitution. It is the law of the land."

Liberal Leader Michael Ignatieff and his team kick off the campaign by insisting a coalition government is not in the cards. Ryan Remiorz/Canadian PressThat's the way things run in countries that have adopted the Westminster system, a democratic parliamentary system of government modeled on what's been in place in the United Kingdom for centuries.

Under that system, if no party wins a majority of seats in an election, the party that wins the most seats gets an invitation from the monarch (the Governor-General in Canada) to form a government. That government gets to govern as long as it can rely on support from enough opposition members to get its legislation through the House of Commons.

If that party can't secure enough support, the Governor-General has two choices: dissolve Parliament and call another election or invite the leader of the party that has won the second greatest number of seats to try to form a government.

The leader of that party can then try to secure the confidence of the House by putting forth a legislative agenda that enough opposition members will support.

Opting to co-operate

There is a third option: a formal coalition, like the one that's governing Great Britain right now. David Cameron's Conservative Party beat Gordon Brown's Labour Party in the May 2010 general election, but fell short of a majority.

Brown negotiated with the third-largest party — the Liberal Democrats — to secure their support as he tried to remain in power. Those talks failed.

Cameron's talks were successful. He negotiated a deal with Nick Clegg — the leader of the Liberal Democrats — that led to Britain's first coalition government since the Second World War.

That deal saw Clegg win the post of Deputy Prime Minister. Four other members of his party were appointed to cabinet. While it is a Conservative government, the Liberal Democrats are a formal part of the government and have a say in the legislative agenda.

Coalition governments have been in place in Canada twice since Confederation. Sir John A. Macdonald was chosen by the coalition government in place to become Canada's first prime minister on July 1, 1867.

In 1917, Conservative Prime Minister Robert Borden attracted enough Liberals to form a coalition known as the "Union Government," which eventually pushed conscription through Parliament. When the First World War ended a year later and the issue of conscription disappeared, the coalition began to fall apart as many of the Liberals who signed on returned to their original party. Some historians argue that this wasn't a true coalition because it did not involve a formal agreement between two parties.

Canada has no roadmap when it comes to how to form a coalition government. The Westminster system, which relies heavily on tradition and unwritten rules, doesn't spell out rules on forming coalition governments. But it clearly allows them.

In 1985, an accord between the Liberals and New Democrats in Ontario led to the end of a four decade-old Progressive Conservative dynasty. However, it was not a coalition government as no New Democrats sat at the cabinet table.

The New Democrats agreed to support the Liberals for two years, as long as the Liberals included certain issues in their legislative agenda. The NDP offered the same deal to the Conservatives, but they turned it down.

The closest Canada has come since the Union Government to a formal coalition was the agreement hammered out between the Liberals and New Democrats in 2008. It was a deal that the Bloc Quebécois said they would support. It was rife with problems, including the fact that the bigger party in the coalition had a leader who already pledged to resign — and tepid support from Michael Ignatieff, the man who was poised to replace him.

The accord that would have formed that coalition would have remained in effect until June 30, 2011.