In the 16th century, the Salamanca School (Francisco Suárez, Francisco de Vitoria, etc.) developed a philosophy of natural law. The law of nature includes, first, some of the most general commandments known to all; and, secondly, certain secondary and more detailed rules, which are, so to speak, conclusions that flow closely from the first principles. As far as these general principles are concerned, the natural law can now be abstractly extinguished from the hearts of men. However, it is extinguished in the case of a particular action, insofar as reason is prevented from applying the general principle to a particular point of practice, because of desire or another passion, as indicated above (77, 2). But what the others, that is, with regard to the secondary commandments, then the natural law can be erased from the human heart, either by bad persuasion, just as in speculative questions errors occur with regard to the necessary conclusions; or by evil customs and corrupt habits, as in some people, theft and even unnatural vices, as the apostle (Rm. i) says, were not considered sins.  The concept of natural law was very important to the development of English common law. In battles between Parliament and the monarch, Parliament often referred to the fundamental laws of England, which were sometimes said to embody the principles of natural law from time immemorial and set limits on the power of the monarchy. However, according to William Blackstone, natural law could be useful in determining the content of the common law and deciding cases of equity, but was not itself identical to English law. Nevertheless, the implication of natural law in the common law tradition meant that great opponents of natural law and advocates of legal positivism, such as Jeremy Bentham, were also virulent critics of the common law. Natural law`s approach to resolving ethical dilemmas begins with the fundamental belief that everyone has the right to live their lives. From there, natural law theorists draw a line between an innocent life and the life of an „unjust aggressor.“ Natural law theory recognizes the legal and moral concept of self-defense, which is often used to justify acts of war.
The strongest construction of the overlap thesis forms the basis of the classical naturalism of Thomas Aquinas and Blackstone. Thomas Aquinas distinguishes four types of laws: (1) the eternal law; (2) Natural law; (3) human rights; and (4) God`s law. The eternal law consists of the laws that govern the nature of an eternal universe; As Susan Dimock (1999, 22) puts it, „the eternal law can be imagined as encompassing all those who are scientific (physical, chemical, biological, psychological, etc.).“ Laws by which the universe is ordered. God`s law deals with the standards that a person must meet in order to attain eternal salvation. Divine law cannot be discovered by natural reason alone; The commandments of God`s law are revealed only through divine revelation. The meaning of „an unjust law is not a law“ is essentially identical to Hart`s „This is a law, but too unjust to be enforced or respected“ (or to be claimed as a defense). The excitement and hostility caused by the earlier way of speaking among modern legal theorists (especially Hart) is unwarranted. No one has difficulty understanding phrases like „an invalid argument is not an argument“, „a disloyal friend is not a friend“, „a charlatan is not a medicine“, etc. „Lex iniusta non est lex“ has the same logic; He acknowledges in his introductory remarks that it is a law on certain important points – perhaps normally and presumably decisive – but then, in its withdrawal or negation of this predicate, asserts that, since justice is the real purpose of being and respecting law, the absence of justice of this particular law deprives it of its decisive importance. who claims to have all the rights. It is therefore law only in a sense that – especially if law, like Hart himself, is regarded as some kind of reason or a presumed reason for action – should be judged as a distorted and secondary meaning, not a central one.
A second category of challenges is metalegal. Natural law theory has always been associated with legal implications that are widely considered counterintuitive. It seems platitude that the requirements of the law can be radically unjust: people do not always have a moral duty to obey the law, complete ignorance of moral facts by a community would prevent these facts from determining the content of its laws. But the theory of natural law, classically conceived, seems to imply the opposite: unjust laws are not laws (Aquinas Summa theologiae); People have a moral duty to obey the law (Finnis, 2011); Moral principles can produce a locally applicable law, regardless of whether or not the relevant principles are transparent to legal subjects (cf. Dworkin 1986). The natural law theorist must either explain why ordinary legal intuition is radically misleading, or show that the implications of the theory are not also revisionist (Atiq to come). Again, how do questions as fundamental as „Should we be right?“ through the positivist thesis „take shape“ that the existence and content of the law depend only on social facts? Doesn`t Green`s assertion reverse the rational order of inquiry and reflection? Basic human needs and circumstances suggest to people, virtually at all times and in all places, that they should establish and maintain certain norms of the kind we call law, norms that depend directly and largely on social facts such as custom, authoritative rule-making, and jurisprudence.