The three powers of the state is a concept articulated by Charles de Secondat, Baron de Montesquieu in his work the Spirit of the Laws. In this work he argued that the three powers a state has are the Legislative, the Executive and the Judicial and that for a state to remain democratic, these powers must be separated and there must be checks and balances to prevent a single group from acquiring control over two or more of them.
This theory provided the basis for the United States Constitution and is the theory behind presidential systems of government. However, in parliamentary systems the role of the legislative and executive branches are merged.
The press is commonly referred to as the fourth power due to its ability to influence and manipulate the political scene by the threat or exercise of its control of the public opinion. The bureaucracy or civil service is also sometimes referred to as a fourth power.