In almost all American states the voters directly choose the nominees of their party in a primary election. The American president is chosen in a national convention, but in about two-thirds of the states the voters directly choose convention delegates committee to a particular presidential candidates. Primary election can simply be defined as an election where the party chooses its candidate or nominee. There are also direct primaries. There are open and closed primaries. Open primaries are open to anyone qualified to vote in the general election. Closed primaries are limited to members registered with a party. The practical difference between the two major categories is that it is relatively easy in open primaries for voters to shift from one party primary to the other, while such shifts are usually more difficult in closed primaries. Not all primaries are equally closed or equally open.
The primary election came into use first in the area where the one-party system was strongest, the southern states, late in the nineteenth century, initially as a result of party rules and later as a result of state law. "The major purpose and effect of the primaries in southern states was to guarantee Democratic control of southern politics" (Malcolm Olsen, pg. 89). Democratic leaders believed that public primaries would legitimate the nominees, settle differences before the general election, and reduce the power of opposition voters. The Democrats were concerned about opposition from both Republican candidates and third parties and about the possibility that such challengers would seek support from black voters.
Outside of the South the campaign for direct primary elections was an important ingredient in the Progressive movement, and it represented a direct challenge to the conservative political leaders who dominated one or both parties in most states. The speed with which this reform spread among the states was impressive.