The separation of powers is an approach to governing a state. Under it, a state's government is divided into branches, each with separate, independent powers and responsibilities so that the powers of one branch are not in conflict with those of the other branches. The typical division is into three branches: a legislature, an executive, and a judiciary, which is the model. It can be contrasted with the fusion of powers in parliamentary and semi-presidential systems, where the executive and legislative branches overlap.
The intention behind a system of separated powers is to prevent the concentration of power by providing for checks and balances.
The separation of powers model is often imprecisely and metonymically used interchangeably with the principle. While the model is a common type of separation, there are governments that have greater or fewer than three branches, as mentioned later in the article.
History  Â
Antiquity  Â
Aristotle first mentioned the idea of a "mixed government" or hybrid government in his work Politics, where he drew upon many of the constitutional forms in the city-states of Ancient Greece. In the Roman Republic, the Roman Senate, Consuls and the Assemblies showed an example of a mixed government according to Polybius .
Early modern mixed government  Â
John Calvin  favoured a system of government that divided political power between democracy and aristocracy . Calvin appreciated the advantages of democracy, stating: "It is an invaluable gift if God allows a people to elect its own government and magistrates." In order to reduce the danger of misuse of political power, Calvin suggested setting up several political institutions that should complement and control each other in a system of checks and balances.
In this way, Calvin and his followers resisted political absolutism and furthered the growth of democracy. Calvin aimed to protect the rights and the well-being of ordinary people. In 1620 a group of English separatist Congregationalists and Anglicans  founded Plymouth Colony in North America. Enjoying self-rule, they established a bipartite democratic system of government. The "freemen" elected the General Court, which functioned as legislature and judiciary and which in turn elected a governor, who together with his seven "assistants" served in the functional role of providing executive power. Massachusetts Bay Colony, Rhode Island, Connecticut, New Jersey, and Pennsylvania had similar constitutions – they all separated political powers.  Books like William Bradford's Of Plymouth Plantation  were widely read in England. So the form of government in the colonies was well known in the mother country, including to the philosopher John Locke . He deduced from a study of the English constitutional system the advantages of dividing political power into the legislative, on the one hand, and the executive and federative power, responsible for the protection of the country and prerogative of the monarch, on the other hand. Â
Tripartite System  Â
During the English Civil War, the parliamentarians viewed the English system of government as composed of three branches - the King, the House of Lords and the House of Commons - where the first should have executive powers only, and the latter two legislative powers. One of the first documents proposing a tripartite system of separation of powers was the Instrument of Government, written by the English general John Lambert in 1653, and soon adopted as the constitution of England for few years during The Protectorate. The system comprised a legislative branch  and two executive branches, the English Council of State and the Lord Protector, all being elected  and having checks upon each other.
A further development in English thought was the idea that the judicial powers should be separated from the executive branch. This followed the use of the juridical system by the Crown to prosecute opposition leaders following the Restoration, in the late years of Charles II and during the short reign of James II .
Montesquieu's separation of powers system  Â
The term "tripartite system" is commonly ascribed to French Enlightenment political philosopher Baron de Montesquieu, although he did not use such a term but referred to "distribution" of powers.
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