Separation of powers
From The Art and Popular Culture Encyclopedia
A theoretical model for governance, common in democratic states, which features the division of sovereign power into at least three (but sometimes up to six) organs of state in order to forestall tyranny, by preventing the acquisition of a monopoly of power by a monarch or oligarchy; also, such an arrangement.
The model was first developed in ancient Greece and came into widespread use by the Roman Republic as part of the uncodified Constitution of the Roman Republic. Under this model, the state is divided into branches or estates, each with separate and independent powers and areas of responsibility. The normal division of estates is into an executive, a legislature, and a judiciary.
Parliamentary democracies do not have distinct separation of powers. The executive, which often consists of a prime minister and cabinet ("government"), is drawn from the legislature (parliament). This is the principle of responsible government. However, although the legislative and executive branches are connected, in parliamentary systems there is usually a independent judiciary.
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 fusion of powers.