Midterms 2026Answers · Third parties
What is Duverger's law, in plain English?
Duverger's law says that when each seat goes to the candidate with the most votes, the system tends to settle into two main parties. It's named after Maurice Duverger, a French political scientist. It's a tendency, not a law of physics, and there are exceptions.
The plain version
Picture an election where whoever gets the most votes wins the seat. Second place gets nothing. Now picture a small party that usually comes in third. Its voters notice that their votes rarely change the outcome. So some of them switch to a bigger party they like a bit less, just to have a say in who wins.
Politicians do the same math. Ambitious people join the parties that can actually win. Donors give to the ones with a shot. Over time, the small party shrinks, and the field narrows to two.
That's the core of it. The way votes are counted nudges everyone toward two choices.
Two effects people point to
- The mechanical effect. Under winner-take-all, a small party can win a decent share of votes spread across the country and get few or no seats.
- The psychological effect. Voters and donors see that, and abandon smaller parties before election day.
Together they make a loop. Fewer votes lead to fewer wins, which leads to even fewer votes.
Where it doesn't hold
Many places with winner-take-all rules still have more than two parties. A party with strong regional support can win seats in its home area while being tiny nationally. That means local strength can break the pattern.
And countries using proportional systems, which split seats by vote share, usually have more parties. That fits the idea that the counting rule is what matters.
Why it matters for the US
The US uses winner-take-all for nearly all House and Senate seats. That's a big part of why two major parties have lasted so long. The names have changed, though. The Republican Party became a major party in the 1850s, as an older party collapsed. So the law explains why there are two, not which two.
My guess is that you'd need either a regional base or a major change in voting rules to break it. Neither is quick.
Where I ran into it myself
When I designed Midterms 2026, my free iPhone game where you found a new party, I wanted the player to feel this pressure. The map shows who leads each state, and the Democrats and Republicans are computer rivals that run attack ads where you get close. You can't just be popular everywhere. You win by getting ahead somewhere.
What to remember
- Winner-take-all elections tend to produce two big parties
- Voters and donors drift away from small parties that rarely win
- Regional strength or different voting rules can break the pattern