Andrew Stark is a professor of strategic management and political science at the University of Toronto.

If the Liberals win the fall election, party leader Justin Trudeau promises it will be the last one Canada holds under its first-past-the-post system. Certainly that system has its flaws. The percentage of the popular vote a party receives is reflected only rarely in the percentage of the seats it holds in Parliament. And so governments – even majority governments – almost never represent a majority of voters, only a plurality.

Under the principal alternative – some form of proportional representation – parties divide the seats according to their share of the popular vote. True, no party will have a majority. After all, a single party almost never wins a majority of votes. And so two or more parties have to coalesce to form a government. But once they do, that government will speak for a majority of voters.

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Would that always be a good thing? Currently, the fact that the government's parliamentary opponents speak, collectively, for an electoral majority gives them a powerful tool, a moral argument always at the ready, to chasten those in power. When Progressive Conservative Mike Harris was premier of Ontario, the opposition was always reminding the government that a majority of the electorate voted against its philosophy. That kind of rhetoric is a central part of Canadian political discourse. It embodies a way of limiting the power of government. Perhaps it is an unintended virtue of our system that the political opposition, far from being the proverbial discrete and insular minority, can – if they want to speak collectively – actually lay claim to the moral status of a majority. In fact, it is a tool they should use more often. Especially when facing a government, like the one in Ottawa, that in its own way has become so discreet and insular.

It is true that our first-past-the-post system involves compromises. We have a mere handful of parties from which to choose. None is likely to reflect fully our individual views, and so we are often forced to make tough internal compromises if we are going to mark a ballot. Parties, too, are organized internal compromises. Because there are relatively few of them, they tend to be "brokerage" institutions. Within the confines of each party caucus, legislators often vigorously debate, coming to decisions that represent a brokering of competing regional and social views.

Proponents of proportional representation say such compromises need not be made, at least not with the same severity. Because every party would get seats in proportion to its share of the popular vote, more parties could find their way into Parliament. Each party would occupy a more defined, less brokered place on the political spectrum. And so voters would be more apt to find a partisan outlet that does a serviceable job of reflecting their genuine views.

But proportional representation does not abolish compromise. Instead of internal compromises by voters and parties, political compromise is simply shifted to external forums that regularly dissolve: legislatures and governments. Once elected, legislators from different parties have to cut deals, diluting their platforms, to form a governing coalition – a coalition that disappears once its members begin fighting each other in the next election.

In a first-past-the-post system, the relationship between compromise and principle is dialectical. Arguments confront counterarguments within the voter's mind or the party caucus, blending into a synthesis that becomes a voter's decision or a party position. Under proportional representation, by contrast, the relationship between compromise and principle is merely cyclical, forming and then coming undone again.

It is a good thing voters have to share much of the heavy lifting of political compromising. And it is not such a good thing that, once having taken a position, a party might abandon or dilute it by making external compromises. Certainly, Canadians are not comfortable with such an idea. Simply consider the fact that the proposed Liberal-NDP-Bloc Québécois coalition deal of 2008 would have allowed disputes between the three to be arbitrated by a "trusted committee of experienced, distinguished Canadians." It is as if the parties knew that they might not be able to do so themselves.

These are deep grains in our political culture. We should reflect cautiously before we do anything that might disturb them.