Electoral and Party Systems: How Voting Rules Shape Parties

Comparing electoral systems

An electoral system is the rule that turns votes into seats.

• First-past-the-post (FPTP): one member per district; whoever gets the most votes wins, even without 50%. Simple and keeps a local link, but seats often do not match votes.
• Electoral college (winner-take-all): each state has electoral votes; the state winner usually takes all of them. A president needs a majority of electoral votes, so it is possible to win the presidency with fewer national votes.
• Party-list PR: seats shared in proportion to votes. Fair to small parties, but voters choose parties, not people.
• Additional Member System (AMS): a mix: some seats by FPTP, others from lists to top up fairness.
• Single Transferable Vote (STV): voters rank candidates 1, 2, 3 in multi-member areas; spare votes transfer.
• Supplementary / two-round systems: if no one gets 50%, a second count or run-off between the top two decides.

Elections differ too: fixed terms vs flexible dates, primaries vs party selection, and how often voters go to the polls.

Two-party and multi-party systems

A party system is how many parties have a real chance of power.

• Two-party system: two parties win almost all seats and take turns in power (USA).
• Two-and-a-half or multi-party: two big parties plus smaller ones that win seats and sometimes join governments (UK at times, India, most of Europe).

Why the USA has a two-party system:

• FPTP and winner-take-all reward only first place (this pattern is called Duverger's law).
• Voters fear a wasted vote and vote tactically.
• Ballot access rules, debate entry rules and campaign costs favour the big two.
• Both big parties are broad "big tents" that absorb new movements.

Party unity, third parties and policies

Internal unity: in parliamentary systems such as the UK, strong whips and the need to keep the government in power make members vote together. In the USA, the separation of powers and primaries give members more freedom, yet in recent years party-line voting has grown with polarisation.

Third parties and independents: in the UK they win more seats than in the USA (for example nationalist parties in Scotland and Wales, and Liberal Democrats), and they run devolved governments. In the USA they mostly influence the agenda or act as spoilers.

Policies: compare parties on the economy, welfare, healthcare, immigration and the environment. Centre-left parties usually favour more public spending; centre-right parties usually favour lower taxes. Parties of the same "side" in two countries can still differ: a centre-right party in a country with free public healthcare may defend that system.

Campaigns and money

Campaigns need money for adverts, staff and travel.

• Strict limits (as in the UK and India): spending caps per candidate and party, bans or limits on paid TV political adverts. Supporters say this keeps elections fair.
• Fewer limits (as in the USA after major court rulings): outside groups can spend large sums. Supporters say spending money is a form of free speech; critics say rich donors gain too much influence.
• Other debates: transparency of donations, digital and social media adverts, and fake news.

Try it: count the seats

Take 5 pretend districts. Write vote shares for three parties in each. Give each seat to the top party (FPTP). Then share 5 seats by total vote share (PR). Compare the two results, then check your thinking with the 3D slider.

Key formulas and definitions

• FPTP: most votes in a district wins the seat
• PR seats ≈ vote share × total seats
• Winner-take-all: the state winner gets all its electoral votes
• Majority needed = more than half of all seats or electoral votes

Worked examples

Common mistakes

• Saying FPTP winners need 50%. They only need more votes than any other candidate.
• Thinking the national vote winner always wins under an electoral college. Winner-take-all can produce a different result.
• Saying PR always leads to weak government. Many PR countries have stable coalitions.
• Assuming the same party label means the same policies in every country.