4.1 Electoral Systems

Electoral systems shape outcomes

Electoral systems are the rules that translate votes into seats. The two main families studied are majoritarian/plurality systems (winner-take-all in single-member districts) and proportional representation (PR) (seats allocated based on vote share). The UK uses First Past the Post (FPTP), while Russia and Mexico use mixed systems combining both.

SMD vs. PR: who wins?

In single-member district (SMD) plurality, the candidate with the most votes wins the seat, even without a majority — this favors large parties and often produces two-party systems (Duverger's Law). PR systems use multi-member districts and party lists, letting smaller parties win seats proportional to their vote share, encouraging multiparty systems and coalition governments.

Consequences for representation

SMD/FPTP tends to produce strong, stable single-party governments but can create disproportionality (a party wins a majority of seats with a minority of votes). PR tends to produce more accurate representation of voter preferences but can lead to fragmented legislatures, coalition instability, and difficulty forming governments, as seen in Iran's and Nigeria's varied systems.

Key terms

Electoral system

The set of rules determining how votes are translated into seats or offices.

First Past the Post (FPTP)

A plurality system where the candidate with the most votes in a single-member district wins; used in the UK.

Proportional Representation (PR)

System allocating seats to parties based on their share of the vote, often via multi-member districts and party lists.

Duverger's Law

Theory that SMD plurality systems tend to produce two-party systems, while PR encourages multiparty systems.

Mixed electoral system

A system combining SMD plurality and PR elements to fill different seats; used in Mexico and Russia.

Try an AP-style question

A single-member district plurality (FPTP) system tends to produce…

1. a single party always
2. many small parties
3. no parties
4. two major parties