There was a lot of fuss when Narendra Modi became the prime minister even though less than a third of those who trudged to the polling booths during the 2014 general election voted for the Bharatiya Janata Party (BJP). The truth is that no Indian prime minister has ever got the top job with the approval of more than half the electorate. Parliamentary majorities are rarely perfect representations of vote share in the voting system that India has.

A similar issue cropped up after Donald Trump began to gain popular support in the months leading to the US presidential election due later this year. There were fears that the voting system in the primaries could help Trump eventually move into the White House. Questions have thus been raised about the way US presidential candidates are chosen.

A few economists have jumped into the debate. They have good reasons to. One fascinating part of economics—social choice theory—shows it is never easy to aggregate the different preferences of individual voters into a coherent collective result that leaves citizens satisfied. In short, there is no perfect voting system in a democracy. The individual choices of millions of voters often get aggregated in puzzling ways.

Two Nobel laureates from Harvard University—Amartya Sen and Eric Maskin—used social choice theory to argue in The New York Times that the way voting in the Republican Party primaries is structured allowed Trump to gain, even though several candidates who stood against him in the primaries might well have beaten him in one-on-one contests. The vote against Trump was split, so he could win the primaries despite getting less than half the votes cast…

India chose the British system of giving a parliamentary seat to that candidate who wins the maximum number of votes, even though more people have collectively voted for other candidates—a system of plurality voting instead of majority voting, in which the winning candidate has to get more votes than all his opponents combined…


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