The purpose of a primary is either private or public.
Partisan primaries have the private purpose of selecting a candidate that best represents the party.
Nonpartisan primaries have the public purpose of selecting a candidate that best represents the people.
Partisan Primaries serve the private purpose of selecting a nominee to represent a political party on the general election ballot. In a partisan primary, voters and candidates participate using different ballots for each party, subject to the access requirements generalized below.
A voter cannot participate in the nomination of party candidates unless they are registered members of that party.
A partisan primary system in which a political party has the option, but not obligation, to allow or disallow unaffiliated voters to participate.
A partisan primary system in which a political party must allow unaffiliated voters to participate.
A partisan primary system in which a voter, regardless of his or her party affiliation, can choose to participate in the party primary of their choice.
Primaries that serve the public purpose of narrowing the candidate field for the general election ballot. In a nonpartisan primary, all voters and candidates participate on the same ballot regardless of party affiliation. All nonpartisan primaries are “open” because no voter is excluded on the basis of their party affiliation.
In a top-two primary, all candidates and voters participate on the same ballot and the top-two vote getters, regardless of party affiliation, advance to the general election.
Often confused with a “top-two” primary, a jungle primary is not actually a primary election. In fact, a jungle “primary” occurs on the same day as the general election, and if a candidate receives 50%+1 or more of the vote, the election is over and that candidate is elected. Only if no candidate gets more than 50%+1 of the vote do the top-two candidates then participate in a head-to-head runoff election.