Differences from a cabinet system

A number of key theoretical differences exist between a presidential and a cabinet system:

• In a presidential system, the central principle is that the legislative and executive branches of government should be separate. This leads to the separate election of president, who is elected to office for a fixed term, and only removable for gross misdemeanor by impeachment and dismissal. In addition he or she does not need to choose cabinet members commanding the support of the legislature. By contrast, in parliamentarism, the executive branch is led by a council of ministers, headed by a Prime Minister, who are directly accountable to the legislature and often have their background in the legislature (regardless of whether it is called a "parliament", a "diet", or a "chamber").
• As with the president's set term of office, the legislature also exists for a set term of office and cannot be dissolved ahead of schedule. By contrast, in parliamentary systems, the legislature can typically be dissolved at any stage during its life by the head of state, usually on the advice of either Prime Minister alone, by the Prime Minister and cabinet, or by the cabinet.
• In a presidential system, the president usually has special privileges in the enactment of legislation, namely the possession of a power of veto over legislation of bills, in some cases subject to the power of the legislature by weighed majority to override the veto. However, it is extremely rare for the president to have the power to directly propose laws, or cast a vote on legislation. The legislature and the president are thus expected to serve as checks and balances on each other's powers.
• Presidential system presidents may also be given a great deal of constitutional authority in the exercise of the office of Commander in Chief, a constitutional title given to most presidents. In addition, the presidential power to receive ambassadors as head of state is usually interpreted as giving the president broad powers to conduct foreign policy. Though semi-presidential systems may reduce a president's power over day to day government affairs, semi-presidential systems commonly give the president power over foreign policy.

Presidential systems also have fewer ideological parties than parliamentary systems. Sometimes in the United States, the policies preferred by the two parties have been very similar (but see also polarization). In the 1950s, during the leadership of Lyndon Johnson, the Senate Democrats included the right-most members of the chamber—Harry Byrd and Strom Thurmond, and the left-most members—Paul Douglas and Herbert Lehman. This pattern prevails in Latin American presidential democracies and the Philippines as well.

Overlapping elements

In practice, elements of both systems overlap. Though a president in a presidential system does not have to choose a government answerable to the legislature, the legislature may have the right to scrutinize his or her appointments to high governmental office, with the right, on some occasions, to block an appointment. In the United States, many appointments must be confirmed by the Senate. By contrast, though answerable to parliament, a parliamentary system's cabinet may be able to make use of the parliamentary 'whip' (an obligation on party members in parliament to vote with their party) to control and dominate parliament, reducing parliament's ability to control the government.

Some countries, such as France have similarly evolved to such a degree that they can no longer be accurately described as either presidential or parliamentary-style governments, and are instead grouped under the category of semi-presidential system.