Legal Jurisprudence: The Theory of Natural Law According to the ancient Greeks, the universe is governed by reason or a rational principle and all humans have reason within them and therefore can know and obey his law. Because human beings have free will, they will not necessarily obey the law if they act according to reason, but they will follow their nature (Halley). So, natural law can be defined as the unwritten law which is almost the same for every human being everywhere in the world. It is the concept of a set of moral principles common to all humanity and recognized by human reason alone. Thus, natural law provides standards for the positive law of a particular society. Aristotle's Natural Law Theory: The Aristotelian view of natural law theory is to reject subjectivism regarding the good, according to which it is somehow perfective or complete of a being, where perfection or completion of a being depends on the nature of a person. So, according to this view, what is good for a tree is what is perfect or perfect for the tree, it depends on the nature of the tree, and what is good for humans is that is what is perfect or perfect for man, according to the nature of the human being. Thus, the fact of the variability of desire is not enough to ask questions about universal goods, because the good is not fundamentally defined by reference to desire. Cicero's Natural Law Theory The Stoic philosophers constructed a universal system based on the concept that all men have the gift of reason and that law is good reason applied to the regulation of human behavior. Cicero in The Republic had presented the best-known formulation of this concept. He said: “The true law is right reason in accordance with nature; it is of universal application, immutable and...... middle of paper ...... that promises must be kept, which in turn is the basis of contract law (Murphy) Trust: l The obligation of trust is the fundamental condition of social harmony. Duties of loyalty arise from principles of natural law and reflect the institutionalization of trust essential to the survival of human association. Conclusion: The United States is a republic founded on the rule of law. Personal liberty rights are better protected here than in any other country in the world. But unfortunately, the law is becoming more and more complex, and it is not easy for ordinary people to plan their conduct in accordance with the law. Intellectual and legal history evolves in cycles, and it is far better for the nation and the country to direct the cycles of ideas toward first principles. This gives us the opportunity to restore the essential framework of the rule of law.