OTTAWA -- If Stephen Harper fails to win a majority on Monday, conventional wisdom suggests he and his Conservative government are toast -- even if they win the most seats.

After all, the leaders of all four opposition parties have been clear there is not "a snowball's chance in hell," as the NDP's Tom Mulcair put it, that they would help prop up a minority Harper government.

With that in mind, Bloc Quebecois Leader Gilles Duceppe has boldly predicted: "Stephen Harper will not be prime minister even if he finishes with the most seats in a minority Parliament."

Not so fast.

There are any number of scenarios that are theoretically possible should no party emerge from Monday's federal election with a majority-- including at least two that could result in a continued Conservative reign.

"We're in the realm of convention here, not formal, written rules and the only rule that really applies is that Parliament must be convened once a year -- so, in principle, (Harper) could extemporize," said Max Cameron, a political science professor at the University of British Columbia's centre for the study of democratic institutions.

That said, minority governments are not uncommon in Canada or other parliamentary democracies and there are conventions which traditionally apply -- as Cameron has helpfully reminded Canadians in a just-released paper, endorsed by 10 of the country's leading political scientists.

How it normally works

In a parliamentary democracy, the leader who can command the confidence of a majority of MPs in the House of Commons becomes prime minister.

If no party wins an absolute majority in an election, the governing party -- in this case, Harper's Conservative party -- has the right to carry on, even if another party actually has more seats, until the prime minister either resigns or is defeated in a confidence vote in the Commons. If a prime minister does not concede defeat, opposition parties get their first opportunity to topple the government by voting against the throne speech, which opens each new session of Parliament.

At that point, it is the prerogative of the Governor General to invite the opposition party with the most seats to form a new government. The new prime minister will have to gain support from one or more of the other opposition parties in order to command the confidence of the House.

That can be done vote by vote, relying on support from different parties at different times -- as Harper himself managed during two successive minority governments. Or support can be attained through some formal or informal agreement with one or more opposition parties to prop up the new minority government for a period of time.

One or more opposition parties could also join together to form a coalition government -- a course of action common in many countries, but rare in Canada.

Though perfectly legitimate, the notion of a coalition has been tainted in Canada by an aborted attempt to unseat Harper shortly after he won a second minority government in 2008.

The Liberals and NDP negotiated an agreement to form a shaky coalition government, but since both parties combined still fell short of a majority, they had to secure a promise of support from the separatist Bloc Quebecois. Further complicating matters, the would-be coalition prime minister, Stephane Dion, had already resigned as Liberal leader.

Harper railed about the affront to democracy, effectively characterizing the coalition as an attempted coup and winning the public relations war. He then persuaded the Governor General to prorogue Parliament, buying himself some time.

By the time Parliament resumed, Dion was gone, the Liberals had gotten cold feet and the coalition agreement fell apart.

How it might work this time

Scenario One: Justin Trudeau's Liberals, who appear to have the most momentum heading down to the wire, win the most seats but fall short of a majority.

Harper has said the party that wins the most seats gets to form government. That's not technically correct, but assuming that remains his political judgment, his government would resign and Trudeau would be invited by the Governor General to form a new government.

Trudeau has consistently ruled out a coalition with the NDP. But should he have a relatively weak minority, Trudeau might be compelled to enter into some formal arrangement to secure the support of New Democrats.

Should Trudeau win a strong minority, it's conceivable the Green party might have sufficient seats to hold the balance of power, in which case Trudeau might come to some co-operation arrangement with Elizabeth May. Given the 2008 experience, Cameron says any coalition or co-operation agreement that involved the Bloc is unlikely to be looked upon with any favour.

More likely, Trudeau would find another more informal way to ensure enough support from one or more opposition parties. Minorities require collegial relations with other parties and can be very productive, notes Cameron; but they can also be short-lived if there is little political will to co-operate.

Scenario Two: Harper wins the most seats. But with no prospect of support from any of the opposition parties, he concedes defeat or waits until his government is toppled in the first confidence vote. The Governor General invites Trudeau to form a government.

Scenario Three: The Conservatives win a minority but rather than concede defeat or wait to be toppled, Harper resigns as leader and delays the resumption of Parliament several months until a new leader can be chosen. He gambles that his party's popularity will improve during a leadership contest and that the public and opposition parties' appetite to defeat his government will abate once he's gone.

Cameron says this scenario is theoretically possible since Parliament doesn't legally have to sit until next June. But normally, he says, Parliament is convened shortly after an election. Should Harper try to delay much beyond mid-November, Cameron predicts there'd be "a hue and cry." That said, Harper has shown a willingness in the past to defy convention.

Scenario Four: The Conservatives win the most seats but are defeated in the first confidence vote on the throne speech. Rather than concede defeat, Harper asks the Governor General to dissolve Parliament and call another election.

That would set the stage for a potential constitutional crisis similar to that which occurred in 1926, when Governor General Lord Julian Byng rejected William Lyon Mackenzie King's request for dissolution and instead called on opposition leader Arthur Meighen to form a government. Meighen's government was swiftly defeated in the House and King won the subsequent election, campaigning against the British Governor General's purported interference in Canadian democracy.

Given the way in which Harper was able to persuade Canadians that the 2008 coalition of "losers" was hijacking democracy, Cameron says it's possible he'd try a similar tactic to pressure the current Governor General, David Johnston, to acquiesce to his demand for another election.

"(Conservatives) have a bigger war chest and they will certainly in those circumstances play victim and could very well try to make the case, 'Look this is all a big conspiracy and it's unfair and it's undemocratic,"' Cameron says.

"The Governor General, however, does have the prerogative to say, 'We don't need to dissolve the House until we've made sure that we can make this Parliament work (under another prime minister).' And given that Canadians have just gone through the longest and most expensive election in our history, I think there would be some public sentiment in support of that."