By André Blais, Université de Montréal*
I examine Duverger’s law according to which « the plurality rule leads to a two party system. » I am interested in the party system at the electoral level, that is, the distribution of votes among the parties. Even though I show that the contemporary evidence tends to disconfirm Duverger’s law, I argue that the basic intuition behind the law is valid.
Duverger predicted that only two parties or candidates would receive a significant degree of support as voters do not want to waste their vote on candidates with little or no chance of winning. This of course assumes that they are short-term utility maximizers and are well informed about the chances of the various candidates.
I examine the outcome of the most recent elections in the three established democracies that use SMP: Britain, Canada, and the United States. I simply count the number of candidates with some minimally meaningful level of support, that is, with at least 5% of the vote.
Table 1 shows the distribution of the number of candidates with at least 5% of the votes in the most recent American (Congressional), British, and Canadian elections. The results are clear. In the U.S. the results almost perfectly support Duverger. There are only two ‘serious’ candidates in 94% of the districts. Things are quite different in Britain and Canada. In both countries, there are only two ‘serious’ candidates in less than 5% of the cases. The most typical situation is to have three candidates with at least 5% of the vote. There are ten times as many cases of four candidates (with at least 5% of the vote) than of two candidates in Canada and twenty times as many in Britain. Hence, Duverger’s law is disconfirmed in Britain and Canada.
I conclude that Duverger’s claim that SMP leads to a two-party system is wrong but that he is absolutely right in arguing that under first past the post a significant number of voters desert their preferred party when it is not viable and that this leads to a less fragmented party system.
André Blais, “Is Duverger’s law valid?” French Politics (forthcoming).
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