Why can proportional-representation systems produce multiparty systems?

Proportional-representation systems tend to produce multiparty systems because they are designed to distribute legislative seats in proportion to the share of the popular vote each party receives. Unlike plurality or majority systems—often called "winner-take-all"—which reward large parties and penalize smaller ones by awarding a constituency's representation to a single candidate, proportional representation ensures that even smaller parties can secure legislative seats.123

This relationship is a core component of what is known as Duverger’s law, which posits that single-member-district plurality systems favor two-party systems, while proportional-representation systems facilitate the development of multiparty systems. Because these systems do not exclude parties that fail to win a majority or plurality in a specific district, they allow for a broader range of political interests to be represented in the legislature. Consequently, in countries utilizing these systems, it is common for three or more parties to hold seats, which often necessitates the formation of coalition governments to achieve a legislative majority.4153