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. The idea that a norm that does not conform to natural law cannot be legally valid is the defining thesis of conceptual naturalism. As William Blackstone describes the thesis: “This natural law, which accords with humanity and is dictated by God Himself, is, of course, superior to all others in obligation. It is binding throughout the world, in all countries and at all times: no human law is valid if it contradicts it; and those who are able-bodied derive all their strength and authority, directly or immediately, from this original” (1979, 41). In this passage, Blackstone articulates the two statements that form the theoretical core of conceptual naturalism: 1) There can be no legally valid norms that contradict natural law; and 2) all valid laws derive their power and authority from natural law. Modern theories of natural law were strongly developed during the Enlightenment, combining the inspiration of Roman law with philosophies such as social contract theory. It was used to challenge the theory of the divine right of kings and became an alternative justification for establishing a social contract, positive law, and government – and therefore legal rights – in the form of classical republicanism. In the first decades of the 21st century, the concept of natural law is closely linked to the concept of natural rights. In fact, many philosophers, jurists, and scholars use natural law interchangeably with natural law (Latin: ius naturale) or natural justice, although others distinguish between natural law and natural law.  To the extent that a definition of law can be given, it must include the idea that the essential function of law is to “realize [social] order by subjecting people`s behaviour to the guidance of general rules by which they can direct their own conduct” (Fuller 1965, 657). The concept of istislah in Islamic law has some similarities with the tradition of natural law in the West, as illustrated by Thomas Aquinas. However, while natural law does consider what is obviously good, since it tends to satisfy the person, istislah generally calls good what is related to one in five “basic goods”.
Many jurists, theologians and philosophers have attempted to abstract these “fundamental and fundamental goods” from legal rules. Al-Ghazali, for example, defined it as religion, life, reason, descent and property, while others also add “honor.” Natural law is a philosophy based on the idea that “good” and “evil” are universal concepts, because humanity perceives some things as useful and good and others as bad, destructive or bad. This means that what constitutes “good” and “evil” is the same for everyone, and this concept is expressed as “morality.” As an example of natural law, it is generally accepted that it is wrong to kill someone, and that it is right and even necessary to punish someone for killing that person. In order to resolve an ethical dilemma using natural law, it is necessary to consider and respect the fundamental belief that everyone has the right by nature to live their own life. From this, natural law theorists determine what an innocent life is and what elements make up the life of an “unjust aggressor.” 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.  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. John Locke incorporated natural law into many of his theories and philosophies, particularly in Two Treatises of Government. There is considerable debate as to whether his conception of natural law resembled that of Thomas Aquinas (filtered by Richard Hooker) or the radical reinterpretation of Hobbes, although the effect of Locke`s understanding is usually formulated in the form of a revision of Hobbes on a Hobbesian contractual basis. Locke reversed Hobbes` recipe, saying that if the ruler violated natural law and failed to protect “life, liberty, and property,” people could rightly overthrow the existing state and create a new one.  Cicero went on to explain natural law as something that can contribute to the common good of society, while 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.
But Thomas Aquinas is also a theorist of natural law. According to him, a human law (that is, what is proclaimed by men) is valid only to the extent that its content corresponds to the content of the natural law; As Thomas Aquinas says, “Human law has as much of the nature of law as natural law. But if it departs from the natural law in any respect, it is no longer a law, but a perversion of the law” (ST. I-II, Q.95, A.II). To paraphrase Augustine`s famous remark, an unjust law is really not a law at all. Early Irish law, An Senchus Mor (The Great Tradition), mentions natural law in a number of places. It is a concept that precedes European legal theory and reflects a type of universal law that can be determined by reason and observation of natural action. Neil McLeod identifies concepts with which the law must agree: for (truth) and dliged (right or claim). Both terms are common, although Irish law never defines them strictly. Similarly, the term córus (law according to the correct order) appears in some places and even in the titles of some texts. These were two very real concepts for lawyers, and the value of a particular judgment against them was apparently verifiable. McLeod also suggested that most of the specific laws mentioned have stood the test of time and have therefore been confirmed to be true, while other provisions are justified in other ways because they are younger and have not been tested over time.
 The laws were written in the oldest dialect of the Irish language. Berla Féini [Bairla-faina], which was so difficult even at that time that the people who were to become Brehons had to be specially instructed there, the time between the beginning and the apprenticeship of a learned Brehon was usually 20 years. Although, according to the law, one in three people could fulfill the duty if both parties agreed, and both were in good health.  It was incorporated into an ethno-Celtic renegade subculture because it has religious overtones and freedom of religious expression allows it to be used again as a valid system in Western Europe.  The Maturidi school, the second largest school of Sunni theology, as well as the Mu`tazilites postulate the existence of some form of natural or “objective” law that people can understand. Abu Mansur al-Maturidi explained that the human mind could know the existence of God and the main forms of “good” and “evil” without the help of Revelation. Al-Maturidi gives the example of theft, which he believes is bad for reason alone, because people work hard for their property. Similarly, murder, fornication and drunkenness are “recognizable evils” that the human mind might experience, according to al-Maturidi.