The plurality vote: must it lead to a 2-party system?
Bennett Marsh, Edwin Baeza, Kenneth Brown, Amberlee Carl
- Introduction
- How do we define a “two-party system”? What makes a party a “major party”?
- Brief discussion of plurality and how it is implemented in real elections
Duverger's Law, attributed by Maurcie Duverger, states that in a system which a plurality vote takes place, with each voter getting a single vote for one candidate, and only a single candidate winning the election, a two-party system will emerge. There are two main reasons for this. They are tactical voting and fusion of minor parties. Tactical voting is when voters tend to change their vote from their top choice candidate to a vote for a stronger party so that their vote is not "wasted". For example, let us suppose that there are 100 voters: 40 prefer an extreme candidate, while the remaining 60 are split 40,20 between two moderate candidates, A and B, respectively. With each voter voting for their top choice, the extreme candidate will win. However, let's assume that the 20 moderate voters would prefer the other moderate candidate over the more extreme one. If these twenty switch their vote from B to A, A candidate wins. If not, the extreme candidate wins, and their vote was "wasted". This will ultimately lead to the collapse of the weaker moderate party, and into a two-party system.
- Tactical Voting - tendency of voters to only vote for the strong parties. No “wasted votes”.
- Fusion of minor parties in an attempt to become stronger
- Real-world examples of the principle occurring in various political systems
- Counterexamples - there exist plurality systems in which there are more than 2 dominant parties
- Converse is not true: 2 party systems may arise even without a plurality election
- Ways of avoiding the collapse into a 2-party system
- Modifications to the standard plurality system
- How a third party can become prominent when 2 dominant parties are already established
- Third parties can exploit weaknesses/mistakes of some major party
- Usually only happens in times of political/social turmoil - e.g. the Civil War
