The Roman jurists developed a method that is not like that of Greek philosophy, modern physics, or economics. Their fundamental concepts were familiar from ordinary experience--for example, possession, fault, and consent. They were not abstracted from experience like substance and accident, mass and energy, or supply and demand, which are understood only by those who have studied philosophy, physics, or economics. The Romans refined and identified these concepts by putting concrete cases. They would move from a concept to its application in a particular case all at once without explaining how they got from the one to the other. In contrast, philosophers, physicists, and economists define their concepts and show their logical implications. It is hard for us to appreciate how different this method is from that of intellectual traditions with which we are more familiar. Historians have imagined that they must have been using some different method, one borrowed from the Greeks. Yet the method was their own, and the concepts to which they applied it are now basic to law in the West and in much of the world besides.