Proponents of separation of powers believe that it protects liberty and democracy, avoiding tyranny. Opponents of separation of powers question whether it indeed does protect liberty, pointing out that it may slow down the process of governing (through gridlock and other means), promote excesses of executive power and unaccountability, and tend to marginalize the legislature.
Parliamentary democracies do not have distinct separation of powers. The executive (often a prime minister) and the Cabinet ("government") are drawn from the legislature (parliament). This is the principle of responsible government. However, although the legislative and executive branches are connected, in parliamentary systems there is usually a independent judiciary.
No democratic system exists with an absolute separation of powers or an absolute lack of separation of powers. Nonetheless, some systems are clearly founded on the principle of separation of powers, while others are clearly based on a fusion of powers.
Montesquieu did specify that "the independence of the judiciary has to be real, and not apparent merely". "The judiciary was generally seen as the most important of powers, independent and unchecked", and also considered the least dangerous. Some politicians decry judicial action against them as a "criminalization" of their behavior, but such "criminalization" may be seen as a response to corruption, collusion, or abuse of power by these politicians.
In fusion of powers, one estate (invariably the elected legislature) is supreme, and the other estates are subservient to it. In separation of powers, each estate is largely (although not necessarily entirely) independent of the others. Independent in this context means either that selection of each estate happens independently of the other estates or at least that each estate is not beholden to any of the others for its continued existence.
Accordingly, in a fusion of powers system such as that of the United Kingdom, first described as such by Walter Bagehot, the people elect the legislature, which in turn "creates" the executive. As Professor Cheryl Saunders writes, "...the intermixture of institutions [in the UK] is such that it is almost impossible to describe it as a separation of powers. In a separation of powers, the national legislature does not select the person or persons of the executive; instead, the executive is chosen by other means (direct popular election, electoral college selection, etc.) In a parliamentary system, when the term of the legislature ends, so too may the tenure of the executive selected by that legislature. Although in a presidential system the executive's term may or may not coincide with the legislature's, their selection is technically independent of the legislature. However, when the executive's party controls the legislature, the executive often reaps the benefits of what is, in effect, a "fusion of powers". Such situations may thwart the constitutional goal or normal popular perception that the legislature is the more democratic branch or the one "closer to the people", reducing it to a virtual "consultative assembly", politically or procedurally unable—or unwilling—to hold the executive accountable in the event of blatant, even boldly admitted, "high crimes and misdemeanors."
Their purpose is to audit government expenditure and general activity.
In the Constitution of Venezuela, the "citizen's power" is a formal branch of government, though it acts like auditors' branches in other jurisdictions.
The press is also sometimes referred to as the Fourth Estate, a term of French origin, which is not related to the modern three-branch system of government.
Originally, the First Amendment of the United States Constitution explicitly guaranteed freedom of the press only against interference by the federal government. Later this right was extended by the United States Supreme Court in the Incorporation Cases to cover state and local governments.
Traditionally, the press has been the "voice of the people", keeping government somewhat in check. Examples of this were the Watergate scandal, where two Washington Post reporters exposed corruption and coverup at the highest levels of government, or the Adscam (Sponsorship scandal) which was uncovered by the press in Canada. This exposure caused the resignation, firing, or prosecution of many officials.
There exist situations where the press can affect public opinion in ways that are contrary to the spirit of separation of powers. One of the most compelling of these situations is when the state controls the content and distribution of the information disseminated by the press. However, even if the press is immune to censorship and compulsion from the government, the controlling entity of a press association or media outlet must almost always edit, and may editorialize, providing opportunities to affect public opinion in ways that may contradict public interest. In all cases, the "voice of the people" (as perceived by some) is modified by the opinions of those producing the stories.
Freedom of the reporting media is generally considered to be essential for the perpetuation of democratic governments, and it is found in all strong democracies, regardless of the organizational principle of the "branches" of government.
Many governments financially support public broadcasting in some way, but in strong democracies these media outlets can enjoy wide editorial latitude.
An independent press acts as a powerful check on all forms of government by providing information about governmental activities to the public. There are weighty arguments to suggest that the press is the external 4th branch which continuously scrutinizes a government's operations, with David Blunkett's two resignations as both Home Secretary(2004) and Secretary of State for Work and Pensions (2005) as particular examples.
Countries with little separation of power include New Zealand and Canada. Canada makes limited use of separation of powers in practice, although in theory it distinguishes between branches of government.
Complete separation-of-powers systems are almost always presidential, although theoretically this need not be the case. There are a few historical exceptions, such as the Directoire system of revolutionary France. Switzerland offers an example of non-Presidential separation of powers today: It is run by a seven-man executive branch, the Federal Council. However, some might argue that Switzerland does not have a strong separation of powers system, as the Federal Council is appointed by parliament (but not dependent on parliament), and the judiciary has no power of review.
It established the three supreme powers as the legislature, executive, and judicial branches, but also created two other autonomous state organs that have equivalent power but not equivalent rank. The first is the Supreme Elections Tribunal (electoral branch) which controls elections and makes unique, unappealable decisions on their outcomes.
The second is the office of the Comptroller General (auditory branch), an autonomous and independent organ nominally subordinate to the unicameral legislative assembly. All budgets of ministries and municipalities must pass through this agency, including the execution of budget items such as contracting for routine operations. The Comptroller also provides financial vigilance over government offices and office holders, and routinely brings actions to remove mayors for malfeasance, firmly establishing this organization as the fifth branch of the Republic.
There is also a judicial branch made up of five supreme courts, state (Länder / Bundesländer) based courts beneath them, and a rarely used senate of the supreme courts.
Due in part to the Republic's youth, the relationship between its executive and legislative branches are poorly defined. An example of the problems this causes is the near complete political paralysis that results when the president, who has neither the power to veto nor the ability to dissolve the legislature and call new elections, cannot negotiate with the legislature when his party is in the minority.
Although the principle of separation of power plays a role in the United Kingdom's constitutional doctrine, the UK constitution is often described as having "a weak separation of powers". For example, in the United Kingdom, the executive forms a subset of the legislature, as does—to a lesser extent—the judiciary. The Prime Minister, the chief executive, must by convention be a Member of the House of Commons and can effectively be removed from office by a simple majority vote. Furthermore, while the courts in Britain are undoubtedly amongst the most independent in the world, the Law Lords, who are the final arbiters of judicial disputes in the UK, sit simultaneously in the House of Lords, the upper house of the legislature, although this arrangement will cease in 2009 when the Supreme Court of the United Kingdom comes into existence. Furthermore, because of the existence of Parliamentary sovereignty, while the theory of separation of powers may be studied in Britain, a system such as that of the UK is more accurately described as a "fusion of powers."
The development of the British constitution, which is not written down in one document, is based on this fusion in the person of the Monarch, who has a formal role to play in the legislature (Parliament, which is where legal and political sovereignty lies, is the Crown-in-Parliament, and is summoned and dissolved by the Queen who must give her Royal Assent to all Bills so that they become Acts), the executive (the Queen appoints all ministers of Her Majesty's Government, who govern in the name of the Crown) and the judiciary (the Queen, as the fount of justice, appoints all senior judges, and all public prosecutions are brought in her name).
The legal mechanisms constraining the powers of the three branches depend a great deal on the sentiment of the people. A common perception is that popular support establishes legitimacy and makes possible the actual implementation of legal authority. National crises (such as the Civil War, the Great Depression, pre-Pearl Harbor World War II, the Vietnam War) have been the times at which the principle of separation of powers has been most endangered, either through official "misbehavior" or through the willingness of the public to sacrifice such principles if more pressing problems are solved. The system of checks and balances is also self-reinforcing. Potential abuse of power may be deterred, and the legitimacy and sustainability of any power grab is hindered by the ability of the other two branches to take corrective action; though they still must actually do so, therefore accountability is not automatic. This is intended to reduce opportunities for tyranny sometimes.
However, as James Madison wrote in Federalist No. 51 regarding the ability of each branch to defend itself from actions by the others, "But it is not possible to give to each department an equal power of self-defense. In republican government, the legislative authority necessarily predominates." Bicameralism was, in part, intended to reduce the relative power of the legislature by turning it against itself, by having "different modes of election and different principles of action." (This is one of the arguments against the popular election of Senators, which was instituted by the Seventeenth Amendment.) But when the legislature is unified, it can obtain dominance over the other branches.
In many American states and local governments, executive authority and law enforcement authority are separated by allowing citizens to directly elect public prosecutors (district attorneys and state attorneys-general). In some states, judges are also directly elected.
Many localities also separate special powers from their executive and legislative branches through the direct election of sheriffs, school boards, transit agency boards, park commissioners, etc.
Juries (groups of randomly selected citizens) also have an important role in the checks-and-balances system. They have the sole authority to not only determine the facts in most criminal and civil cases, but to judge the law, acting as a powerful buffer against arbitrary enforcement by the executive and judicial branches. In many jurisdictions they are also used to determine whether or not a trial is warranted, and in some places Grand Juries have independent investigative powers with regard to government operations.
It can be argued that there is no natural distinction between executive and legislative forms of government: legislation that is passed must always be executed, and much executive action requires new laws. As such, the division can be said to be an artificial one. This is borne out by the fact that there is currently no constitutional system which has a complete separation of powers where there is a distribution of the three functions among three independent organs with no overlapping or cross-coordination. Some of the early American States and the French Constitution of 1791 tried to enforce this doctrine strictly, but they failed. Instead, most constitutions give slightly overlapping powers to each branch, such as the US president's ability to veto legislation, or the power of judicial appointment.
Some observers believe that no obvious case exists in which such instability was prevented by the separation of powers. In parliamentary systems such as the United Kingdom the three "powers" are not separated (although the judiciary is independent). However, this has not threatened British stability, because the strong tradition of parliamentary sovereignty serves the purpose of limiting executive power.
In contrast, many countries which have adopted separation of powers (especially in Latin America) have suffered from instability (coups d'etat, military dictatorships, civil war and unrest, etc). If the separated executive is granted strong powers, it may well encourage instability, because it is less consensus-oriented than a parliamentary system, and because it inures the population and political elite to a the influence of a dominant leader. In times of instability, competing political groups can become obsessed with controlling the executive office, and it is often the loss of a presidential election which triggers greater instability. In a presidential system, there can only be one winning party, and all others fail entirely to gain power. In contrast, a parliamentary system can allow all political groups to have some share in control of the executive by participating in a coalition.
Alternatively, if the executive branch is granted few powers, there is the danger of political gridlock. When the executive cannot control or cannot operate alongside the legislature, then government action to solve society's problems can be limited.
Political scientists have also noted the tendency for separation-of-power systems, especially those with strong executives, to develop into two-party systems . As the executive is as a "winner-take-all" position, voters and lobby groups tend to adopt a strategy of supporting their preferred choice from the two leading candidates, the perception being that a vote or donation to a third-party candidate is a waste. As the executive is usually considered the most important position in government, members of the legislature will coalesce into groups supporting the two dominant executive candidates.
The categories of the functions and corresponding powers of government are inclined to become blurred when it is attempted to apply them to the details of a particular constitution. Some hold that the true distinction lies not in the nature of the powers themselves, but rather in the procedure by which they are exercised.
Sometimes systems with clearly defined separation of powers are difficult for the average person to understand, resulting in a nebulous political process and leading to a lack of engagement. Proponents of parliamentary systems claim that they make it easier to understand how "politics is done" by providing a clearer view of who does what, who is responsible for what, and who is to blame. This is important when it comes to engaging the people in political debate and increasing citizens' interest and participation in politics. However, for a parliamentary system to work effectively, institutional arrangements such as fair electoral laws, freedom of the press, independent courts, due process, and the independence of the Houses of Parliament must be so designed as to prevent executive supremacy over the legislative and judicial branches while also encouraging a culture of public debate, open government, accountable office holders, and policy contest-ability and compromise, rather than a culture of "winner takes all" political domination.