Civics GovernmentHow Electoral Systems Shape Representation
Justice stands at a large whiteboard covered in district maps and vote tallies inside a civic classroom, drawing arrows between vote percentages and seat counts while students lean forward, debating why a party that won 40% of votes ended up with 60% of seats.
- Explain the difference between winner-take-all using a plurality rule (first-past-the-post) and proportional representation electoral systems.
- Identify how each system translates votes into legislative seats using real numeric examples.
- Compare how first-past-the-post and proportional systems affect party diversity and voter incentives.
- Predict which system is more likely to produce a two-party legislature versus a multi-party legislature and explain why.
- Evaluate a trade-off between electoral simplicity and accurate representation of voter preferences.
Key terms
- First-past-the-post
- A single-member plurality rule awarding a district's seat to the candidate with the most votes.
- Proportional representation
- A system distributing legislative seats roughly in proportion to each party's share of the vote.
- Duverger's Law
- The tendency of single-member plurality districts to produce a stable two-party system over time.
- Electoral threshold
- A minimum vote share, often around five percent, a party must reach to win any PR seats.
- Wasted vote
- A ballot that elects no one, common under plurality rules for losing or third-party candidates.
How Rules Translate Votes Into Seats
The same ballots yield different legislatures depending on the counting rule. First-past-the-post asks only who leads in each district, so a party with 40% support concentrated across many districts can capture a majority of seats while a party with broad but thinner support wins almost none. Proportional representation instead allocates seats nationally or regionally to mirror vote shares, so a 20% party earns roughly 20% of seats. The rule, not just voter preference, determines who governs — which is why constitutional designers treat the electoral formula as a deliberate, high-stakes choice.
Incentives and Their Costs
Each system shapes how parties and voters behave. Under FPTP, rational voters abandon third parties to avoid wasting a vote, the dynamic Duverger's Law describes, producing two big-tent parties and clear single-party majorities but leaving large minorities unrepresented and creating uncompetitive safe seats. Proportional representation keeps small parties viable, mirrors preferences more faithfully, and usually requires coalition government, at the cost of slower bargaining and fragmentation. Thresholds add a further wrinkle, so even PR is not perfectly proportional. The honest comparison weighs representational accuracy against governing simplicity.
Worked examples
Compute the FPTP winner in a split district.
- List the shares: Party X 34%, Party Y 33%, Party Z 33%.
- Apply the plurality rule: the largest share wins the single seat.
- Identify Party X as the leader with 34%.
- Note that 66% of voters preferred someone else, yet no majority is required.
Answer: Party X wins the seat outright despite being opposed by 66% of voters.
Allocate 100 PR seats by vote share.
- Take the vote shares: A 45%, B 35%, C 20%.
- Apply proportional allocation to a 100-seat chamber.
- Assign approximately 45, 35, and 20 seats respectively.
- Note a threshold could bar a very small party, so results are near-proportional, not exact.
Answer: Roughly 45, 35, and 20 seats, mirroring each party's vote share.
Activity
Distribute 120 votes across three parties in a 6-seat legislature and calculate seat outcomes under both systems
Practice
Predict whether a single-member plurality system produces two parties or many, and explain why.
Explain one tradeoff a country accepts by choosing proportional representation over first-past-the-post.
Common mistakes to avoid
- Proportional representation is perfectly fairThresholds, rounding, and coalition bargaining cause PR results to deviate from pure vote-share proportionality.
- Every district system creates two partiesDuverger's Law applies to single-member plurality districts, not to two-round or proportional systems.
Check your understanding
In a first-past-the-post election for a single legislative seat, Party X wins 34% of the vote, Party Y wins 33%, and Party Z wins 33%. What happens?
A student argues: 'Under proportional representation, small parties always get exactly the seats they deserve, so it's a perfectly fair system.' Which critique best challenges this claim?
Duverger's Law predicts that which type of electoral rule tends to produce a two-party system over time?
Recap
Electoral rules are not neutral: first-past-the-post produces two-party majorities but wastes minority votes, while proportional representation mirrors preferences yet invites coalitions; thresholds and rounding mean no system is perfectly proportional, so each trades accuracy against simplicity.
Reflect
Which value matters more to you in an electoral system, accurate representation or decisive governance?