The hidden dangers of two-party politics

In a two-horse race, declines in popularity for one candidate are equivalent to gains in popularity for the other, writes doctor of mathematics Kit Yates

There are sound mathematical reasons why two parties battling it out – a duel so to speak – is not good for democracy (Parliament Live)

With local elections upon us, many voters feel like they are faced with the same old tired choice between the two major political parties – Labour and the Conservatives.

Despite the existence of third candidates, election leaflets come through the door telling us “Lib Dems can’t win here” – effectively arguing the case for a straight fight between the two major parties in British politics. But, as we look forwards to the general election next year, there are sound mathematical reasons why two parties battling it out – a duel so to speak – is not good for democracy.

In a two-horse race, declines in popularity for one candidate are equivalent to gains in popularity for the other. If it is harder to boost one’s own image than it is to denigrate the other party, then the incentive is for the parties to batter each other with negative advertising, leaving the electorate to choose between a rock and a hard place. The introduction of a genuinely electable third party can change the campaigning dynamics from a straight duel to a “truel” – a battle between three parties.