The functions of the government are vast and varied. It is necessary to entrust these functions to specific organs, so that the responsibility for performing these functions may be effectively fixed. The division of governmental power under any constitutions may be of two kinds; the functional division such as legislative, executive and judicial and the territorial division of federalism.
Thus structurally considered government consists of three branches having for their functions (i) legislation or law meaning (ii) their execution or administration and (iii) interpretation of these laws. The three branches to which these functions belong are known as the Legislature, the Executive and the Judiciary respectively. Political liberty in a state is possible when restraints are imposed on the exercise of these powers. The functions of the government should be differentiated and assigned to separate organs to limit each section to its own sphere of action. So that these organs independently interact between themselves. This is what is known as the theory of separation of powers. ORIGIN OF S.O.P.- ARISTOTLE
Its origin can be traced back to Aristotle, the father of Political Science. Of course he did not discuss the issue in great details. He only analysed the functions of the three branches of government, the deliberative, executive and the judiciary without suggesting their separation. JOHN LOCKE’S THEORY.
John Locke was one of the eighteenth century philosophers to pay greater attention to the problems of concentration of governmental power. He argued that the executive and legislative powers should be separate for the sake of liberty. Liberty suffers when the same human being makes the law and executed them. MONTESQUIEU’S THEORY.
He in his book "The Spirit of Laws" published in 1748 gave the classic exposition of the idea of separation of powers. Montesquieu, a great advocate of human dignity, developed the theory of separation of powers as a weapon to uphold the liberty of the people. He believed that the application of this theory would prevent the overgrowth of a particular organ which spells danger for political liberty.
According to him every man entrusted with some power is bound to misuse it. If the same person or body of persons exercise these three powers that of enacting laws, executing them and of trying the cases of individuals, he maintained, that could spell the doom of the whole system of governance. In simple words Montesquieu's view is that concentration of legislative, executive and judicial functions either in one single person or a body of persons results in abuse of authority and such an organisation becomes tyrannical. He argued that the three organs of government should be so organized that each should be entrusted to different persons and each should perform distinct functions within the sphere of power assigned to it.