Just imagine when a theist and an atheist live in a desert. The theist prays with strong faith whereas the atheist denies God and the hereafter. Hence, since the atheist does not believe in divine law, he will not avoid evils. But for a peaceful life, they still have to comply with a set of rules; though need not embrace each other’s religion. This is the natural law which inspires them the moral values for their own survival. So, natural law does not necessarily belong to a particular group, but to all mankind regardless of their faith or religion.
Greek philosophy emphasized the distinction between “nature” on the one hand and “law”, “custom”, or “convention” on the other. What the law commanded varied from place to place, but what was “by nature” should be the same everywhere.
It is aptly said, “All those things to which man has a natural inclination are naturally apprehended by reason as being good and, consequently, as objects of pursuit, and their contraries as evil and objects of avoidance. Wherefore the order of the precepts of the natural law is according to the order of natural inclinations. “
Natural law first appeared among the stoics who believed that God is everywhere and in everyone. Within humans is a “divine spark” which helps them to live in accordance with nature. The stoics felt that there was a way in which the universe had been designed and natural law helped us to harmonize with this.
Aristotle and others argued that each kind of animal has a mental nature that is appropriate to its physical nature. All animals know or can discover what they need to do in order to lead the life that they are physically fit to live. Thus humans are naturally capable of knowing how to live together and do business with each other without killing each other. Humans are capable of knowing natural law because, in a state of nature, they need to be capable of knowing it.
The best evidence of Aristotle’s having thought there was a natural law comes from the Rhetoric, where Aristotle notes that, aside from the “particular” laws that each people has set up for itself, there is a “common” law that is according to nature. Specifically, he quotes Sophocles and Empedocles:
Universal law is the law of Nature. For there really is, as everyone to some extent divines, a natural justice and injustice that is binding on all men, even on those who have no association or covenant with each other. It is this that Sophocles Antigone clearly means when she says that the burial of Polyneices was a just act in spite of the prohibition: she means that it was just by nature:
“Not of to-day or yesterday it is, but lives eternal: none can date its birth.”
And so Empedocles, when he bids us kill no living creature, says that doing this is not just for some people while unjust for others:
“Nay, but, an all-embracing law, through the realms of the sky Unbroken it stretcheth, and over the earth’s immensity.”
“There is in fact a true law - namely, right reason - which is in accordance with nature, applies to all men, and is unchangeable and eternal.” Cicero says.
Cicero, a Roman philosopher and politician, writes that both justice and law derive their origin from what nature has given to man, from what the human mind embraces, from the function of man, and from what serves to unite humanity. For Cicero, natural law obliges us to contribute to the general good of the larger society. The purpose of positive laws is to provide for “the safety of citizens, the preservation of states, and the tranquility and happiness of human life.” In this view, “wicked and unjust statutes” are “anything but ‘laws,’” because “in the very definition of the term ‘law’ there inheres the idea and principle of choosing what is just and true.” Law, for Cicero, “ought to be a reformer of vice and an incentive to virtue.” Cicero expressed the view that “the virtues which we ought to cultivate, always tend to our own happiness, and that the best means of promoting them consists in living with men in that perfect union and charity which are cemented by mutual benefits.”
In asking whether there is an eternal law, Thomas Aquinas, an Italian Dominican friar and priest, begins by stating a general definition of all law: Law is a dictate of reason from the ruler for the community he rules. This dictate of reason is first and foremost within the reason or intellect of the ruler. It is the idea of what should be done to insure the well ordered functioning of whatever community the ruler has care for.
“The good is to be done and pursued and evil is to be avoided” is not very helpful for making actual choices. Therefore, Aquinas believes that one needs one’s reason to be perfected by the virtues, especially prudence, in order to discover precepts of the Natural Law that are more proximate to the choices that one has to make on a day to day basis.
At the end, I would like to quote John Foster Dulles as he states, “Economic and military power can be developed under the spur of laws and appropriations. But moral power does not derive from any act of Congress. It depends on the relations of a people to their God. It is the churches to which we must look to develop the resources for the great moral offensive that is required to make human rights secure, and to win a just and lasting peace.”