"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."
"The different governments will control each other, at the same time that each will be controlled by itself."
Source: Federalist #51 by James Madison.

What Enlightenment idea of Montesquieu's does this quote refer to?