Separation of powers principle

The separation of powers, is a model for the governance of a state. Under this model, a state's government is divided into branches, each with separate and independent powers and areas of responsibility so that the powers of one branch are not in conflict with the powers associated with the other branches. The typical division is into three branches: a legislature, an executive, and a judiciary, which is the trias politica model. It can be contrasted with the fusion of powers in some parliamentary systems where the executive and legislative branches overlap.

Separation of powers, therefore, refers to the division of responsibilities into distinct branches to limit any one branch from exercising the core functions of another. The intent of separation of powers is to prevent the concentration of unchecked power and to provide for checks and balances to avoid or inefficiencies.

The separation of powers model is often imprecisely and metonymically used interchangeably with the trias politica principle. While the trias politica is a common type of this form, it is not its only type.

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 (Histories, Book 6, 11–13).

John Calvin (1509–1564) favoured a system of government that divided political power between democracy and (mixed government). 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 which should complement and control each other in a system of checks and balances.

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