AP® Comparative Government and Politics · Unit 4 · Topic 4.1
The Same Votes Run Through Different Systems
The rule that converts votes into seats is not neutral. Run the same ballots through first-past-the-post versus proportional representation and you get a different legislature each time, because each system makes a different choice about what "fair" means.
An electoral system is just a formula for translating votes into seats, and no formula is neutral. First-past-the-post, also called plurality, gives every district's seat to whichever candidate gets the most votes there, even without a majority. Winners take all, losers get nothing, and small differences in vote share can turn into huge differences in seats, often rewarding the largest party with a seat share bigger than its vote share. Proportional representation instead allocates a party's seats to match its national vote share as closely as possible, so a party with 30 percent of the vote gets roughly 30 percent of the seats.
Picture 100 voters splitting 40, 30, 20, and 10 percent across four parties. Run through many small plurality districts, the 40 percent party can sweep most seats and govern alone. Run through pure proportionality in one 100-seat chamber, the result is close to 40, 30, 20, and 10 seats, and no party can govern without a coalition. Same votes, opposite legislatures, because the rule did different work on them.
This is why no one can call either outcome the neutral reflection of what voters wanted. Plurality is built to manufacture decisive, governable majorities; proportional representation is built to mirror the electorate's divisions honestly. Each trades something away, stability for accuracy or accuracy for stability. That same design choice keeps surfacing with district boundaries: redraw the lines around fixed votes, and seat totals shift again, which is why mapmaking is never a technical afterthought.
Key terms
- First-past-the-post
- A plurality system where the candidate with the most votes in a district wins the seat outright, regardless of majority.
- Proportional representation
- A system that allocates a party's seats to match its share of the national or regional vote.
- Seat share versus vote share
- The percentage of legislative seats a party holds compared to the percentage of votes it won.
- Proportional entitlement
- The number of seats a party would receive if seats were assigned strictly according to its vote share.
- Hung parliament
- A legislature in which no single party holds enough seats to govern alone, often forcing a coalition.
Watch it explained
- How it worksWalk me through 100 identical votes converted to seats by plurality, then by proportional rules.
- Worked exampleShow me parties on 40, 30, 20, and 10 percent turned into a legislature three different ways.
- Worked exampleFind the seat totals in a 100-seat chamber under first-past-the-post and then under pure proportionality.
- Common mistakeWhy isn't there a neutral electoral system that simply reflects what voters wanted?
- Going furtherWhat happens to the result when you keep the votes fixed and only redraw the district lines?
Check yourself
End of topic.