Presidential and parliamentary systems are the main types of democratic political systems. Parliamentary system implies formation of government (headed by a prime minister) by a party or a party coalition which has received the majority in the government. Presidential system involves direct presidential elections, regardless of legislative branch of government. Parliamentary and presidential systems also differ in terms of correlation of executive and legislative powers. In the first type, parliament plays the major part in the state; in the second type, the president is both the head of state and the head of government. The president, as well as parliament, is elected by the people.
In a parliamentary system, parties play significant role in politics, although deputies should not act on behalf of their parties, which are only a part of society, but represent the whole nation. Main benefits of a parliamentary system are viewed in its ability to respond to changes and its flexibility. Parliamentary systems, especially if they are elected through proportional elections, have a tendency for pluralism when even small political groups are represented in the legislative body. As a result even smallest minorities can participate in political process on the highest level. Such variety stimulates cooperation and compromise, which can be observed when parties form governing coalition. If coalition falls apart or party loses its mandate to govern, the prime minister resigns, and a new government is formed, or a new election is held. Nonetheless, this does not necessarily cause a crisis dangerous for a democratic political system. However, the main disadvantage of parliamentary system is instability, which is the reverse side of flexibility and participation in governance. Multiparty coalition can be unsteady and fall apart at the first signs of crisis. Government can be manipulated by extremist groups and parties to conduct certain political campaigns by threatening the government to leave the coalition which might cause resignation of the government. Another result of parliamentary political system is that the prime ministers can sometimes be just political leaders without the necessary authority possessed by politicians, elected by the people. Another cause of concern is lack of formal institutional limitations of parliamentary superiority. A political party which possesses the majority in the parliament can pass serious bills without efficient limitations, which can turn out to be tyranny of the majority.
Presidential system is characterized by direct accountability, durability and power. Presidents chosen by the people can have the authority which results from direct elections, regardless of status of their party in the parliament. By establishing real and theoretically equal branches of government, a presidential system tries to establish powerful executive and legislative institutions, which check and balance each other. If president and legislators represent different parties and cannot reach compromise they might prevent bills of the opposing side from being passed, i.e. by exercising veto right. This is why the president has to reach an agreement with the legislative body, regardless whether it is controlled by opposition or not. Party discipline is significantly weaker in presidential system; for instance, presidents cannot remove party members from office or call them to order, which can be easily done by prime ministers. A prime minister with strong majority can guarantee passing of governmental bill. On the other hand, a president, who arduously guards own prerogatives, has to conduct long negotiations with parliament before passing the important bill.
Question about which of the two systems, parliamentary and presidential, is the most efficient for democracy and which one corresponds most accurately to the requirements of the democratic political system, still remains open. This is a permanent issue for debates among political scientists, sociologists, philosophers, politicians, etc. as both systems have their own advantages and disadvantages.