Portrait of James Madison

James Madison on the need for the “separation of powers” because “men are not angels,” Federalist 51 (1788)

Found in: The Federalist (Gideon ed.)

In Federalist Paper no. 51, James Madison (1751-1836) worries about how to create institutions which would check personal ambition and the "encroachment" of one branch of government by the other

Politics & Liberty

But the great security against a gradual concentration of the several powers in the same department, consists in giving to those who administer each department, the necessary constitutional means, and personal motives, to resist encroachments of the others… Ambition must be made to counteract ambition. The interest of the man, must be connected with the constitutional rights of the place. It may be a reflection on human nature, that such devices should be necessary to control the abuses of government.