Separation of powers, a term coined by French political Enlightenment thinker Baron de Montesquieu, is a model for the governance of democratic states. The model is also known as Trias Politica.
The model was first developed by the ancient Greeks in the constitutions that governed their city-states. However, it first came into widespread use by the Roman Republic. It was outlined in the Constitution of the Roman Republic.
Under this model, the state is divided into branches or estates, and each estate of the state has separate and independent powers and areas of responsibility. The normal division of estates is into the Executive, the Legislative, and the Judicial.
Proponents of separation of powers believe that it protects democracy and forestalls tyranny. Opponents of separation of powers question whether it accomplishes this end, and point out the success of mingling powers in parliamentary democracies. Furthermore critics have pointed out that, regardless of whether it accomplishes the end of forestalling tyranny, it may slow down the process of governing, promote executive dictatorship and unaccountability, and tend to marginalize the legislature.
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 mingling of powers.
