Who would have thought the New Democratic Party would be taking its place as the Official Opposition as the House of Commons resumed Sept. 19? Not the Liberal Party, that is for sure, nor the Bloc. Perhaps the most surprised are the closest observers of parliament: the press gallery and the national media.

Now that the “how did this happen” stage of reporting is over, the prominent storyline is that as the Official Opposition the NDP must get serious and moderate its traditional policy stances. Major political figures and players in the national media like a scenario where the New Democrats recognize their past limitations, become more centrist, and work with the Liberals.

Canadian party politics has been described as either a one-party dominant system: the natural governing party; or as a two-party system: the ins and the outs. Stephen Harper is doing everything in his power to make the Conservatives the new natural governing party, taking over the role occupied for so long by the Liberals.

Traditionally what most separated the Liberals and Conservatives was that one party held power, and the other power wanted power. In his classic book on Canadian political parties (recent editions co-edited with Alan Whitehorn) the esteemed Queen’s political scientist Hugh G. Thorburn referred to this alternating two-party political system ( the ins and the outs) as the Tweedledee-Tweedledum vision of Canadian parties. The two-party view excluded “third” parties such as the NDP altogether, though an amended theory did allow for a two-and-one-half party system.

The NDP was founded 50 years ago on the premise it could be the one dominant party. That idea looked down right laughable until last the last election moved the NDP into the official opposition role. The NDP did play an important role in the 1960s and early 1970s, supplying policy ideas to the dominant Liberal party, thus taking on the one-half role, in the two-and-one-half party view of Canadian politics.

The one dominant party, and the two-party theories are close cousins since each allows for an in-power party, and an out-of-power party. But, the two-party theory suggests the parties are virtually interchangeable, without people noticing that much difference between them on major questions. The one-party dominant theory allows for ideological change when a new dominant party arises.

Today, no one doubts that Stephen Harper aims to use his majority to build Conservative Party strength at the expense of the Liberals. His road to establishing one-party dominance requires the Liberals to be forced out of contention for power. For example, the prime minister’s graceful gesture to Olivia Chow in suggesting a national funeral for Jack Layton, also allowed for wider public recognition of how the NDP has replaced the Liberals as the out-of-power party.

Harper welcomes the sharp contrast between his Conservatives championing a strong pro-business orientation, and New Democratic critics of big business excess. What he prefers to keep hidden is that his party equates business with “owners” of business. For New Democrats economic enterprises have to be held responsible to customers, employees, and the community, not just shareholders.

A keen ideological contest suits both parties, since each is convinced of its eventual success. However, a real battle of ideas does not leave much of a place for the Liberals.

One Liberal, former Prime Minister Jean Chrétien, wants to block the Harper plan to make the Conservatives the one dominant party, by having the NDP and the Liberals merge their efforts. Chrétien, a serious Liberal partisan for over 50 years, has a big will to win, something that as his biographer Lawrence Martin showed, triumphs over most other considerations, including in this instance, partisanship. The street fighter in Chrétien understands that the split in public support between his Liberals and the New Democrats facilitates the Harper drive for one-party dominance.

Putting Liberals and New Dems together is problematic. Many New Democrats are happy to call themselves socialists. Few Liberals would want that name. Serious differences in how people think about and experience the world divide the two parties; not enough to rule out a forming a coalition government together, at least from the NDP side.

The Ignatieff Liberals preferred not to take power with the NDP, in part because it meant abandoning the phony war with the Bloc, who had agreed to support the coalition.

The NDP got to where they are today because in Quebec the party offered a way forward for Quebecers who were tired of the federalists versus sovereignists debate featuring Liberals and the Bloc.

As a party of the left, the NDP has a great deal in common with the Bloc, and with the provincial Québec Solidaire. By focusing on the economic and social concerns of Quebecers, the NDP came out of nowhere to win 59 of 75 seats.

No one should be surprised if the New Democrats continue to fight for their traditional concerns in this coming parliamentary session. That is what Quebec voters expect, and winning Quebec is what makes the party credible politically outside Quebec. New Democrats will have serious trouble with playing Tweedledum to the Conservative Tweedledee.

Duncan Cameron is the president of rabble.ca and writes a weekly column on politics and current affairs.