Natural law is a set of rules derived from the nature of human beings. For many lawyers, this ordinance, which derives from the existence of powers and duties common to all men, it is necessary, unchanging and unchangeable. These legal scholars argue further that the right to life, the right to freedom, the right to equality and resistance to oppression is self-evident rules. Also argue that they are the basis of positive law and it is formed by the specific rules that originate from the different sources of law, ie law, custom, jurisprudence and doctrine or legal theory. The Natural Law, ie, the authors postulate the existence of natural law, say the positive law can not contradict the precepts of the first order.
For some historians, the theory of natural law was given by Eastern thinkers, Greek and Roman antiquity. However, this thinking was defended primarily by Catholic philosophers and jurists, who claimed to be based on divine revelation. From the eighteenth century, some authors put forward a rational root natural right. Positivist legal thought began to be exhibited in the nineteenth century. The most renowned of the writers of this school is the Austrian Hans Kelsen U.S. citizen, a university professor in Vienna, Harvard and Berkeley. In its pure theory of law and the State (1945), the author argued that the rules are rules that are associated penalties for that are no longer met. For Kelsen no basis outside of the rules of positive law. On the basis of the regulatory systems there are other rules, which generally are the Constitutions of the States, over which are the basic rules of international law.