Changing political, social, economic, and intellectual conditions over the past two hundred years have demanded innovation and adjustment of legal doctrine, thus giving the United States Constitution a character which the framers of the document could not have predicted. Historically, one must not only understand developments since 1787 but also the roots of the constitutional system reaching down to a colonial base in the two centuries before 1787. Three principles from our constitutional past (popular sovereignty, federalism, and the rule of law) have innumerable applications, express faith as well as ascertainable fact, and have a breadth transcending the American experience. Popular sovereignty, the principle that governments derive their power from the consent of the governed; federalism, the division of power between a central authority and regional-local levels; and the rule of law, meaning a just government operating within the constraints of the legal system, all persist; at the same time, they are in some respects interpreted differently now than in former generations. The living Constitution of 1986 may differ from the text written in 1787, but the framers themselves made it possible. They felt it necessary and desirable to write a brief, open-ended document which would not have survived two hundred years if it had been long, detailed, and impossible to change. (APG)