Law is an order of human behavior. An order is a system of rules. Law is not, as it is sometimes said, a rule. It is a set of rules having the kind of unity we understand by a system. It is impossible to grasp the nature of law if we limit our attention to the single isolated rule.

General Theory of Law and State (1949), I. The Concept of Law, A. Law and Justice, a. Human Behavior as the Objects of Rules