John Adams in "A Dissertation on the Canon and Feudal Law" (1765):
[L]iberty cannot be preserved without a general knowledge among the people, who have a right ... to knowledge ... and a desire to know; but besides this, they have a right, an indisputable, unalienable, indefeasible, divine right to that most dreaded and envied kind of knowledge, I mean, of the characters and conduct of their rulers. Rulers are no more than attorneys, agents, and trustees for the people; and if the cause, the interest and trust, is insidiously betrayed, or wantonly trifled away, the people have a right to revoke the authority that they themselves have deputed, and to constitute abler and better agents, attorneys, and trustees...The stale, impudent insinuations of slander and sedition, with which the gormandizers of power have endeavored to discredit your paper, are so much the more to your honor; for the jaws of power are always opened to devour, and her arm is always stretched out, if possible, to destroy the freedom of thinking, speaking, and writing…
James Madison in Federalist #47:
The accumulation of all powers, legislative, executive, and judiciary, in the same hands, whether of one, a few, or many, and whether hereditary, self-appointed, or elective, may justly be pronounced the very definition of tyranny.
George Washington in his Farewell Address (1796):
It is important, likewise, that the habits of thinking in a free country should inspire caution in those entrusted with its administration, to confine themselves within their respective constitutional spheres, avoiding in the exercise of the powers of one department to encroach upon another.The spirit of encroachment tends to consolidate the powers of all the departments in one, and thus to create, whatever the form of government, a real despotism. A just estimate of that love of power, and proneness to abuse it, which predominates in the human heart, is sufficient to satisfy us of the truth of this position.The necessity of reciprocal checks in the exercise of political power, by dividing and distributing it into different depositaries, and constituting each the guardian of the public weal against invasions by the others, has been evinced by experiments ancient and modern; some of them in our country and under our own eyes. To preserve them must be as necessary as to institute them.
Excerpts from an excellent article by Hume's Ghost on Unclaimed Territory