The second thesis, which is at the heart of the moral theory of natural law, is the assertion that moral norms are somehow derived or implied by the nature of the world and the nature of man. St. Thomas Aquinas, for example, identifies the rational nature of man as what defines the moral law: “The domination and measure of human actions is reason, which is the first principle of human action” (Thomas Aquinas, ST. I-II, Q.90, A.I). Since humans are rational beings by nature, it is morally appropriate that they behave in a manner consistent with their rational nature. Thus, Thomas Aquinas draws the moral law from the nature of man (i.e. from the “natural law”). Empirically, many moral theorists of natural law are also theorists of natural law, but the two theories are, strictly speaking, logically independent. One can deny the theory of natural law, but advocate a theory of morality of natural law. John Austin, the most influential of the early legal positivists, for example, denied the overlap thesis but advocated something similar to an ethical theory of natural law. Liberal natural law emerged from medieval Christian theories of natural law and Hobbes` revision of natural law, sometimes in a disturbed balance between the two.
Because of the intersection between natural law and natural law, natural law has been claimed or attributed as a key element in the United States Declaration of Independence (1776), the France Declaration of the Rights of Man and of the Citizen (1789), the United Nations Universal Declaration of Human Rights (1948). and the European Convention on Human Rights (1953) of the Council of Europe. Hobbes` version is, “Do not do this to others that you would not have done to yourself.”  The seven “fundamental goods” defined by the natural system of justice are: life, procreation, education, worship or search for God, social life, avoiding offense and avoiding ignorance. Laws also have a purpose: to create justice. From the point of view of natural law, a law that does not ensure justice (an unjust law) is considered “no law at all.” Therefore, a law that is imperfect is a law that no one should follow. In short, every law that is good is moral, and every moral law is good. Legal positivism is a theory of law that is the opposite of natural law theory. Legal scholars believe that a law can be deeply flawed and yet can be considered a law. This dilemma is a good example of the principle of double action. A double effect occurs when a traditionally “good” action leads to a “bad” outcome or an outcome that is best avoided according to the principles of natural law. For example, administering strong painkillers to a terminally ill patient is a “good” act because it makes the patient feel better.
If the drug also causes the death of the patient faster, the principle of double action applies as the right action (pain relief) justifies the wrong result (death). However, making room for a new patient in the hospital does not in itself justify killing the terminally ill patient. Among the founders who inspired Justice Thomas to consider natural law an integral part of the American judicial system, Thomas Jefferson referred to it when he wrote in the first paragraph of the Declaration of Independence: Subsequently, Cicero explained natural law as something that can contribute to the general good of society, whereas positive law would contribute to the security of society. Many contributions to natural law theory continued to be made, such as during the Renaissance and the Enlightenment. This led to the creation of more modern theories of natural law, combining natural law with other philosophical theories such as social contract theory. Although this task is generally interpreted as an attempt to analyze concepts of law and the legal system, there is some confusion as to the value and character of conceptual analysis in legal philosophy. As Brian Leiter (1998) points out, philosophy of law is one of the few philosophical disciplines that considers conceptual analysis to be its primary concern; Most other areas of philosophy have taken a naturalistic turn, incorporating the tools and methods of science. To illustrate the role of conceptual analysis in law, Brian Bix (1995) identifies a number of different purposes that conceptual claims can serve: (1) to pursue the use of language; (2) establish service documents; (3) explain what is important or essential about a class of objects; and (4) establish an evaluation test for the word term. Bix assumes that conceptual analysis in law focuses on (3) and (4). Natural law consists of those commandments of the eternal law that govern the conduct of beings who possess reason and agency.
The first commandment of natural law, according to Thomas Aquinas, is the somewhat empty imperative to do good and avoid evil. Here it should be noted that Thomas Aquinas advocates a theory of the morality of natural law: what is right and wrong according to Thomas Aquinas derives from the rational nature of man. Thus, good and evil are both objective and universal. It is claimed that the theory of natural law existed without even needing human understanding or any kind of political order or legislation. To be explained further, natural law involves the idea that humans intrinsically understand the difference between “good” and “evil.” In essence, he concludes that humans are not taught about natural laws; They initiate it by making good and good decisions. Therefore, it is said that it can be found by the exercise of reason. Adam Smith postulated the following three natural laws of economics:1. Law of Self-Interest – It allows people to take charge of their growth and development.2. Competition Law – It explains how competition fosters the development of high-quality products.3. Law of supply and demand – It states that production must increase as long as costs remain low.
The term “natural law” derives from the belief that human morality comes from nature. Everything in nature has a purpose, including man. Our goal, according to natural law theorists, is to live a good and happy life. Therefore, actions that run counter to this purpose – that is, actions that would prevent another human being from living a good and happy life – are considered “unnatural” or “immoral.” The important things that [conceptual naturalism] supposedly allows us to do (for example, to morally evaluate the law and determine our moral obligations to the law) are actually complicated by the collapse of the distinction between morality and law. If we really want to look at law from a moral point of view, it can obscure the task if we consider that law and morality are essentially linked. Moral criticism and legal reform may be supported by initial moral skepticism of the law. The best proof that Aristotle thought there was a law of nature comes from rhetoric, where Aristotle states that in addition to the “special” laws that each people has established, there is a “common” law that corresponds to nature.  Specifically, he quotes Sophocles and Empedocles: Natural law was originally defined by ancient Greek philosophers such as Aristotle and Plato. Plato had no theory of natural law; However, some of his theories included concepts of natural law. On the other hand, Aristotle focused on the distinction between law and nature. This then led to the introduction of natural justice, which can be attributed to the Stoics. Man is not taught natural law per se, but we “discover” it by constantly making decisions for good rather than evil.
Some schools of thought believe that natural law is transmitted to man by a divine presence. Natural law theory is defined as universal laws of nature that govern concepts of morality and justice such as good and evil and good and evil.