 America has a two-party voting system. But why? Do Americans just hate third parties? It's actually not that simple. Duvergé's law, developed by French political scientist Maurice Duvergé in the 50s, suggests that the way we vote is the strongest influence on the number of parties, not a lack of third-party interest. The way we vote? How else would we do it? Voting is simple. You get your choices, you pick one, and whoever gets the most votes wins. Actually, there are many ways of voting that most people haven't even heard of. To properly look at Duvergé's law, we're going to have to think outside of the box. Duvergé's law has two main factors. Factor one, how many votes does it take to win a seat? And factor two, are people encouraged to vote for their favorites, even if it doesn't look like they'll win? These may seem obvious, but we haven't looked at how things could be different yet. In America, we use a single-winner voting method called plurality voting, meaning you only get to pick one candidate for one position, and we elect people within single-member districts. A winner takes all system. Let's take a look at our first factor, threshold. How many votes does it take to win? Easy, right? Whoever has the most votes? This is obviously harder on smaller parties. What this means for winner takes all districts is that a party within that district has either the most support or no representation in government at all. There's no middle ground. And per Duvergé's second factor, plurality voting is hard on small parties because of voter psychology. With only one choice, people don't vote for smaller parties, even if the candidate is their favorite candidate. That's because nobody wants to waste their vote, or, even worse, throw the election to a candidate they hate, the infamous spoiler effect. Now, all of this has been kind of obvious so far. We can see how plurality voting gives no chance and no representation to third parties. But let's look at some other voting methods. Approval voting is still a single-winner voting method, but it doesn't limit you to only one choice. Instead, your vote allows you to express all the candidates you want, who you approve of. Instead of being forced to choose between an ideal candidate or a safe candidate, voters can pick them both or more without compromising. This addresses Duvergé's second factor, the psychological problem of voting against your favorite. So now, third parties can get an accurate measure of their support. However, it only halfway addresses Duvergé's law because it is still within a winner takes all system with a high-winning threshold and nothing for smaller parties. To actually give smaller parties a chance, you need proportional representation. Proportional representation is a particular class of multi-winner voting methods. Instead of multiple single-winner districts, you combine them into multi-winner districts. Then, you assign seats based on the total vote proportions, not which candidate has the most within each district. A party with 50% of the votes will get 50% of the seats, but even a party with 30% or 20% could still get seats, assuming enough seats are being elected. This addresses both parts of Duvergé's law. In proportional voting, you don't need a plurality to win a seat, you only need a proportion. Since the threshold is lower, it's easier for smaller parties to get seats, and since it's easier to get seats, people feel more comfortable voting for their favorite candidates. Proportional representation beats both parts of Duvergé's law and gives smaller parties representation. So let's recap. In winner takes all districts, plurality voting is difficult to win for third parties, discourages voting for smaller parties, and rarely has minority representation. Approval voting lets you vote for multiple candidates, but it is still winner takes all. Proportional representation solves those problems by both lowering the threshold for seats and encouraging more honest voting. That combination provides representation for smaller parties. Obviously, there are other influences on the number of parties besides Duvergé's law, such as ballot access, geographic concentrations, or unique political issues. But for the most part, we can conclude that plurality voting encourages a two-party duopoly. Approval voting helps third parties by letting voters support their honest favorites, and proportional representation encourages an actual multi-party system.