(This is an archived page, from Edition 2 of the Patterns of Power book. The current versions is at https://www.patternsofpower.org/patterns/legal/elements/separation/).
M.J.C. Vile defined the doctrine of separation of powers as follows:
“A "pure doctrine" of the separation of powers might be formulated in the following way: It is essential for the establishment and maintenance of political liberty that the government be divided into three branches or departments, the legislature, the executive, and the judiciary. To each of these three branches there is a corresponding identifiable function of government, legislative, executive, or judicial. Each branch of the government must be confined to the exercise of its own function and not allowed to encroach upon the functions of the other branches. Furthermore, the persons who compose these three agencies of government must be kept separate and distinct, no individual being allowed to be at the same time a member of more than one branch. In this way each of the branches will be a check to the others and no single group of people will be able to control the machinery of the State.”
[The above use of the word ‘government’ is a potential source of confusion here – it is used where this book would refer to ‘governance’.]
He went on to say that "the doctrine has rarely been held in this extreme form, and even more rarely been put into practice" but it is nonetheless a powerful safeguard and might be considered as an objective worth taking into account.
The ‘executive’ in Vile’s terminology is the government, or the Administration in American terminology, and the mechanisms for forming a government depend upon the political system (6.1.2). It has direct control over the law enforcement agencies and the penal system – which both form part of the Legal Dimension. The executive itself is bound by the rule of law in most countries, as part of their Constitutions.
The legislature, in a liberal democracy, is elected and is under political control but is usually separate from the executive. In America, the two houses of Congress are separate from the Administration and act as a check on the power of the President. In Britain, the two houses of Parliament act as a check on the power of the government (though ministers, including the Prime Minister, are members of Parliament). In both cases there is a limit on the power of the government to create new legislation – so that it cannot, for example, reduce individual freedom without the consent of the majority of the democratically elected representatives of the people. Other democracies, and other types of government, have differing degrees of separation between the legislature and the executive.
An executive has to be decisive in the short term, acting on behalf of the people, but a legislature has to represent the diversity of the people and take a longer-term view of society's interests; it also has the effect of acting as a check on the executive's political powers.
The separation between the judiciary and the executive ensures that the latter obeys the rules. The executive must not be 'above the law'. This is especially important in the case of the law enforcement agencies, for which the executive is responsible. A separate judiciary provides an impartial judgement to ensure that the law enforcement agencies do not break the law when bringing cases to trial. And, as noted previously (18.104.22.168), the judiciary is better placed than politicians to consider individual cases.
The separation between the legislature and judiciary, within the Legal Dimension, is a safeguard to ensure the impartiality of justice, so that a judge cannot invent law on a personal whim but is bound by a separately authorised body of rules. The argument in favour of balancing power towards the legislature is that there is political control over it in a liberal democracy, whereas the populace has no direct say in the appointment of judges. The counterargument is that a legislature with a temporary political majority should not easily be able to make laws to undermine civil rights which were established by due process at an earlier time – so judges should have the power to prohibit legislation which breaches the Constitution or agreements with other countries.
The separation of powers is an important safeguard for human rights against oppression, particularly where rights have been agreed at a supra-national level; without it, a government can suppress opposition and victimise individuals without any checks or hindrances. There are many examples of governments making laws that prohibit dissent and then keeping themselves in power by imprisonment, torture or execution of their opponents. As American Founder James Madison wrote:
“The accumulation of all powers, legislative, executive, and judiciary, in the same hands, whether of one, a few, or many, and whether hereditary, selfappointed, or elective, may justly be pronounced the very definition of tyranny.” 
Each country has to determine an appropriate balance of power between its executive, its legislature and its judiciary.
© PatternsofPower.org, 2014
 M.J.C. Vile, Constitutionalism and the Separation of Powers, p. 14.
 Burma (Myanmar) is a prime example of an authoritarian regime that imposes its will by abuse of legal coercion. A small example is the following:
“Feb 28, 2008 (DVB), The Burmese government's newly-approved referendum law has banned monks and prisoners from voting, and made campaigning against the referendum punishable by up to three years in prison.”
This came from an article on the Democratic Voice of Burma website, and was available in May 2014 at http://www.dvb.no/uncategorized/referendum-law-excludes-monks-and-bans-dissent/1086.