natural law ethic for the political scene, which includes the concept of natural rights and deals with violence and non-violence in interpersonal relations. Rothbard criticizes contemporary political scientists for neglecting this task and engaging in positivistic and empiricist approaches that lack explicit ethical judgments. He also criticizes present-day political philosophers for confining themselves to antiquarian descriptions and exegeses of past philosophers, rather than justifying value positions relevant to politics. Rothbard calls for a return to natural law and natural rights standards to establish a political philosophy of liberty and the proper sphere of law, property rights, and the state. Part II: A Theory of Liberty Part II, "A Theory of Liberty", is "the substance of the work itself", and outlines Rothbard's ethical theories. It contains chapters 6 through 21. These chapters have been divided into subsections for the benefit of Wikipedia readers, although Rothbard did not do so. Property, exchange, and aggression Chapter 6, "A Crusoe Social Philosophy", introduces the concept of "Crusoe Economics," which is the analysis of an isolated man in nature, and argues that it has an indispensable use in economics and social philosophy. Rothbard believes that by examining a man isolated from society and interactions with other people, the fundamental truths of human nature can be better understood. Crusoe's needs and desires must be fulfilled by transforming the natural world around him into capital and consumer goods through labor and reason. Rothbard argues that reason is unique to humans and is essential to survival and achievement. Crusoe's rationality leads him to learn about his ends and how to attain them, and he can do so through observation, abstraction, and thought. Chapter 7, "Interpersonal Relations: Voluntary Exchange", explains that "the process of exchange enables man to ascend from primitive isolation to civilization", and that exchange is "made possible by two primordial facts of nature—natural laws—on which all of economic theory is based: (a) the great variety of skills and interests among individual persons; and (b) the variety of natural resources in geographic land areas." Additionally, Rothbard notes that exchange benefits both the weak and the strong, as it allows them to specialize and exchange for mutual benefit. Rothbard also explains that what is really being exchanged is not the commodities themselves, but the rights to ownership of them. Finally, he explains the importance of a generally accepted medium of exchange, or money, which is indispensable for any