Ambition must be made to counteract ambition. — James Madison

Madison, James. "No. 51: How to maintain: make the parts check each other. Also, a federal system divides power further.--Madison (or Hamilton)." The Federalist: A Commentary on the Constitution of the United States, edited by Robert Scigliano. The Modern Library, 2001.

Madison, James [published as Publius]. "Federalist No. 51, The Structure of the Government Must Furnish the Proper Checks and Balances Between the Different Departments." New York Packet, 8 Feb. 1788.