In the government of this commonwealth, the legislative department shall never exercise the executive and judicial powers or either of them: the executive shall never exercise the legislative and judicial powers, or either of them: the judicial shall never exercise the legislative and executive powers, or either of them: to the end it may be a government of laws and not of men.
—Massachusetts Constitution. Drafted by John Adams, Samuel Adams, and James Bowdoin, ratified June 15, 1780, it is the oldest written constitution in the world.
The separation of powers is a vital aspect of the rule of law. Without it, the distinction between making and deciding the law is lost, returning government to the days when tribal chieftains decided disputes according to their impulses. William Paley explained:
The first maxim of a free state is, that the laws be made by one set of men, and administered by another; in other words, that the legislative and judicial characters be kept separate. When these offices are united in the same person or assembly, particular laws are made for particular cases, springing oftentimes from partial motives, and directed to private ends: whilst they are kept separate, general laws are made by one body of men, without foreseeing whom they may affect. (The Principles of Moral and Political Philosophy, 1785.)