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 American legal system is based on natural law theory, which states that the primary purpose of all people is to live a «good, peaceful, and happy» life, and that the circumstances that prevent them from doing so are «immoral» and should be eliminated.
In this context, natural law, human rights, and morality are inextricably linked in the American legal system. The methodological approach assumes less substance about morality than the master-rule approach requires. But this requires us to take advantage of an interesting and rich knowledge of the properties of basic goods. Whether this information is available is controversial. But the methodological approach has the advantage of firmly anchoring natural law arguments in favor of moral principles in the goods that the pursuit of these moral principles is supposed to regulate. Acts of violence such as murder defeat our «human purpose» to lead a good life. Therefore, throwing over injured passengers is an unnatural act and violates natural law. Even if their deaths would ensure the survival of the other 22 passengers, the murder is against our human nature. Natural law prohibits the killing of injured passengers in all circumstances. A law against murder is a just law according to the theory of natural law. Although natural law applies primarily to the field of ethics and philosophy, it is also widely used in theoretical economics. In contrast to the multitude of Hobbes` laws, Cumberland states in the very first sentence of his treatise on the laws of nature that «all the laws of nature are reduced to one, benevolence towards all rationals.»  He later clarified, «By the name of rational, I ask permission to understand God and man; and I do so under the authority of Cicero.
Cumberland argues that the mature development («perfection») of human nature involves individual human will and action for the common good.  For Cumberland, human interdependence excludes the natural Hobbes right of each individual to wage war on all others in order to survive personally. Here are some examples of concepts that emerge in natural law theory and the applications of these concepts: Natural law concerns companies from an ethical point of view, where they should not deceive their customers or other stakeholders. For example, the marketing of drugs should be done with full disclosure of potential harms and not be sold as snake oil. 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. Natural law theory can be difficult because of the changing nature of human belief and ethics.
What was considered unethical is now considered necessary. What was once considered good and correct behavior is now considered terribly unethical. In this activity, students think about how to deal with a situation where the law may be vague. While Locke spoke in the language of natural law, the content of that law largely protected natural rights, and it was this language that later liberal thinkers favored. Political philosopher Jeremy Waldron pointed out that Locke`s political thought was based on «a certain set of Protestant Christian assumptions.»  For Locke, the content of natural law was identical to biblical ethics as enunciated particularly in the Decalogue, the teaching of Christ, and exemplary life. Recently, there are non-theistic writers in the tradition of natural law who deny (1): see, for example, the works of Michael Moore (1982, 1996) and Philippa Foot (2001). There have been a number of post-Thomistic authors in the Middle Ages and in modern times who, in some way (2), denied the natural authority of natural law and asserted that if the content of natural law is wholly or partially determined by human nature, its receptivity can only come from an additional divine command: the views of John Duns Scotus, Francisco Suarez and John Locke fit into this form. The Stoics may have been thinkers of natural law, but they seem to deny (4) and have the right to stand before the good ones (see Striker 1986).
Some contemporary theological ethicists called «proportionalists» (e.g. Hallett 1995), have taken up and denied the point of view of natural law with a consequentialist turn (6). (For a discussion of the relationship between proportionalism and natural law theory, see Kaczor 2002.) And while some view Aristotle as the source of the natural law tradition, others have argued that his central appeal to person-insighted practical wisdom as the ultimate measure of right action excludes the possibility of the kind of general rules that (at least in a theistic context) would make Aristotle`s ethics a natural legal position.