If men were angels, no government would be necessary. If angels were to govern men, neither external nor internal controls on government would be necessary. In framing a government which is to be administered by men over men, the great difficulty lies in this: you must first enable the government to control the governed; and in the next place oblige it to control itself.
James Madison, Federalist Papers Nos. 10 and 51
checks-and-balances, government, separation-of-powers