"And what country can preserve its liberties, if its rulers are not warned from time to time that this people preserve the spirit of resistance ? Let them take arms ... The tree of liberty must be refreshed from time to time, with the blood of patriots and tyrants."
-- Thomas Jefferson
[letter to William S. Smith, 1787, in Jefferson, On Democracy 20, S. Padover, ed., 1939 ]
((mainly included for the detailed source))