In a parliamentary vote, politicians seek the support of other members of parliament to pass laws and form a government. They do this by forming political parties that campaign and compete for seats in the legislative body, which can be a unicameral (one-chamber) or bicameral (two-chamber) chamber. A party with a majority of seats votes for its own leader, who then forms the cabinet and leads the executive branch.
Most parliamentary systems, including the UK and Canada, use a plurality electoral system whereby voters cast as many votes as there are positions to be filled (the first-past-the-post or winner-takes-all system). In other systems – such as single non-transferable vote in multimember constituencies, used in the US before the 1960s; or the Single Transferable Vote or PR system used in Japan before 1994 – votes are counted on a preferential ballot, with voters ranking their preferred candidates in order of preference. A candidate must receive a certain number of first preferences, the ‘quota’, to win a seat. Surplus votes are then ‘transferred’ to the second or subsequent choices of voters, until all seats are filled.
Walter Bagehot, a 19th-century English economist, praised parliamentary governments for producing serious debates, allowing for a change of power without an election, and permitting elections to be held at any time. This contrasts with the four-year term for presidents in a presidential system.
However, a key weakness of the parliamentary system is that the legislative body is not subject to any check or balance by the head of state, unlike in a presidential system, where a new bill requires approval from the monarch or governor general before it takes effect. In addition, a head of state may ‘veto’ laws passed by the legislature through a ceremonial act that simply returns the bill to parliament for reconsideration.