Montesquieu

Democratic and aristocratic states are not in their own nature free. Political liberty is to be found only in moderate governments; and even in these it is not always found. It is there only when there is no abuse of power. But constant experience shows us that every man invested with power is apt to abuse it, and to carry his authority as far as it will go. Is it not strange, though true, to say that virtue itself has need of limits?

To prevent this abuse, it is necessary from the very nature of things that power should be a check to power. A government may be so constituted, as no man shall be compelled to do things to which the law does not oblige him, nor forced to abstain from things which the law permits.

Charles de Secondat, Baron de Montesquieu, The Spirit of the Laws (De l’esprit des loix; 1748), Book XI, “Of the Laws Which Establish Political Liberty, with Regard to the Constitution.”