- Direct mandate — in a presidential system, the president is often elected directly by the people. To some, this makes the president's power more legitimate than that of a leader appointed indirectly. In the United States, the president is elected neither directly nor through the legislature, but by an electoral college.
- Separation of powers — a presidential system establishes the presidency and the legislature as two parallel structures. Supporters claim that this arrangement allows each structure to supervise the other, preventing abuses.
- Speed and decisiveness — some argue that a president with strong powers can usually enact changes quickly. However, others argue that the separation of powers slows the system down.
- Stability — a president, by virtue of a fixed term, may provide more stability than a prime minister who can be dismissed at any time.
Advantages of a parliamentary system
Some believe that it is easier to pass legislation within a parliamentary system. This is because the executive branch is dependent upon the direct or indirect support of the legislative branch and often includes members of the legislature. Thus, this would amount to the executive (as the majority party or coalition of parties in the legislature) possessing more votes in order to pass legislation. In a presidential system, the executive is often chosen independently from the legislature. If the executive and legislature in such a system include members entirely or predominantly from different political parties, then stalemate can occur. Former US President Bill Clinton often faced problems in this regard, since the Republicans controlled Congress for much of his tenure. Accordingly, the executive within a presidential system might not be able to properly implement his or her platform/manifesto. Evidently, an executive in any system (be it parliamentary, presidential or semi-presidential) is chiefly voted into office on the basis of his or her party's platform/manifesto. It could be said then that the will of the people is more easily instituted within a parliamentary system.
In addition to quicker legislative action, Parliamentarianism has attractive features for nations that are ethnically, racially, or ideologically divided. In a unipersonal presidential system, all executive power is concentrated in the president. In a parliamentary system, with a collegial executive, power is more divided.
It can also be argued that power is more evenly spread out in the power structure of parliamentarianism. The premier seldom tends to have as high importance as a ruling president, and there tends to be a higher focus on voting for a party and its political ideas than voting for an actual person.
In English Constitution praised parliamentarianism for producing serious debates, for allowing the change in power without an election, and for allowing elections at any time. Bagehot considered the four-year election rule of the United States to be unnatural.
There is also a body of scholarship, that claims that parliamentarianism is less prone to authoritarian collapse. These scholars point out that since Second World War , two-thirds of Third World War countries establishing parliamentary governments successfully made the transition to democracy. By contrast, no Third World presidential system successfully made the transition to democracy without experiencingcoups and other constitutional breakdowns. As Bruce Ackerman says of the 30 countries to have experimented with American checks and balances, "All of them, without exception, have succumbed to the nightmare [of breakdown] one time or another, often repeatedly."
A recentWorld Bank study found that parliamentary systems are associated with lower corruption.