Hayek's theory of liberty cannot be rightly understood from the doctrine presupposing the priority of right. The paper proposes, instead, another principle demanding the rule of law as necessary and the fulfillment of knowledge-efficiency as sufficient conditions to demonstrate his political doctrine. How to discover, utilize and spread the knowledge of circumstances in society is the core conception which runs through Hayek's academic thoughts, and which is literally the key to understanding his early as well as later theses of political concern, and trying to delimit an ideal borderline for the rule of law which confines the sphere of liberties.