"He was vowing to replace Canada’s electoral system, which tended to give parties power disproportionate to their level of support"
PR advocates believe that each party should have a number of MPs proportionate to the votes that party has received; but the relationship between power and proportion of MPs is inherently nonlinear.
Simple models:
1.Consider an assembly with 100 members. If party A has 45 votes, party B has 40 votes and party C has 15 votes, which party is most powerful? They are all equal because any two parties voting together has a majority.
Imagine party A has a majority of members: in one case it has 85 votes, and another it has 55 votes. In which case is it more powerful? A party with a majority has the same amount of power whether or not it is an overwhelming majority.
(Those models neglect that in some matters an assembly may require an enhanced majority, say 2/3 or unanimity. Also members of an assembly need not vote en bloc.)
#ProportionalRepresentation necessarily leads to party power disproportionate to level of popular support. As a consequence, we must evaluate the merits of electoral systems on other criteria.
@mpjgregoire Interesting point, but I think you're missing the fact that parties are not simply interchangeable. E.g. if party A is centrist, party B is far-right and party C is far-left, it's unlikely that B and C will cooperate to defeat A. Ok, it's not just left/right, but parties will tend to cooperate with others whose policies are similar. Also voters will tend to shift between like-minded parties, so in general, popular policies are likely to be implemented. #proportionalrepresentation
In Canada we have three main political parties: the Conservatives on the right, the NDP on the left and the Liberals in the centre. Imagine an election under a PR system in which the Liberals and the Conservatives tie at around 45% of the vote — Canadians seem to desire a centre-right government, no? But in fact the 10% NDP members are likely to form a governing coalition with the Liberals and pull policy to the left since their support is essential.
@mpjgregoire Ok, in that scenario it would be more logical for the Liberals and Conservatives to cooperate, but of course politics is not always rational. There's no perfect system, but PR still looks much better than FPTP on balance.
@CGM Indeed, every system has its failings, and in the end no democratic system can be much better than its electorate. But I think if you look at it by its results, you'll see that FPTP works better than many people interested in political ideas realise.
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