Answer:
1) The Enlightenment idea of Montesquieu's that this quote refers to is the idea that a government should be divided into separate branches, each with its own area of responsibility.
2) When James Madison says that our government is "obliged to control itself," he is referring to the system of checks and balances that was designed to prevent any one branch of government from having too much power.
3) An example of how checks and balances are seen in our government today is the fact that the president cannot make laws without the approval of Congress, and Congress cannot override the president's veto without the approval of the Supreme Court.
4) "Checks and balances" is a system in which each branch of government has the power to check the actions of the other branches, in order to prevent any one branch from having too much power. This system was designed by the Enlightenment thinker Montesquieu.