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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 by providing for "checks" and "balances" to avoid autocracy, over-reaching by one branch over another, and the attending efficiency of governing by one actor without need for negotiation and compromise with any other.

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 model, there are governments which utilize bipartite, rather than tripartite, systems as mentioned later in the article.

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