People sometimes use the phrase "moral compass" to describe the innate sense of right and wrong that human beings have. President Obama, for example, recently mentioned in one of his speeches how we need to, "keep our own moral compass pointed in a true direction." Although he didn't spell out what that true direction might be, his remark nevertheless highlighted something that all can agree upon, namely, the importance of being guided by a moral compass.

When functioning properly, this moral compass (a.k.a. our "conscience"), not only encourages us from within to "do good and avoid evil," but also sets off internal alarm bells when we are tempted to carry out evil acts. Some acts, such as murder, torture, theft, and adultery will trigger those alarm bells almost universally, irrespective of time period, culture, or upbringing within a particular society.

No society erects statues to honor their greatest adulterers, or to celebrate their most prolific murderers. When a genocidal leader is cast in marble, it is to memorialize qualities like courage or leadership, not his murderous proclivities.

The fact that certain actions like murder and adultery are wrong and invariably harmful, and readily perceived as such, leads to what is known as the "Natural Law." The Natural Law signifies that we can know through our powers of reason what is right and wrong, and that our reason can thereby guide us towards an ethical life. Becoming aware of the Natural Law through a carefully formed moral compass is an essential part of what it means to be human. Those who invoke Natural Law appeal to self-evident principles that can be known by all humans.

Catholic teachings about morality also rely on the notion of Natural Law. The Second Vatican Council, to consider but one example, describes our moral duty this way: "Deep within his conscience man discovers a law which he has not laid upon himself but which he must obey."

The Natural Law, nonetheless, is not a specifically Christian idea, but has its origins in pre-Christian thought. Several Greek philosophers discuss the notion. Cicero, the Roman lawyer and writer (106-43 B.C.), has a famous passage wherein he describes the Natural Law:

"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. By its commands it summons men to the performance of their duties; by its prohibitions it restrains them from doing wrong. To invalidate this Law by human legislation is never morally right, nor is it permissible ever to restrict its operation; and to annul it wholly is impossible."

He also notes how the Natural Law cannot be "one thing at Rome, and another at Athens; one thing today, and another tomorrow; but in all times and nations this universal law must forever reign, eternal and imperishable."

Despite its constancy and universality, the demands of the Natural Law are not easily specified or deduced, free of disputation or debate. Some people today, in fact, influenced by the hedonism and relativism of our age, would go further and outright deny the existence of the Natural Law.

Interestingly, though, whenever a serious crisis or threat to civilization arises, the validity of natural law reasoning tends to reassert itself. Such a resurgence occurred, for example, at the end of World War II, during the Nuremberg trials and in the prosecutions against those who had perpetrated heinous crimes against humanity. Nazi defendants objected to being placed on trial for simply following the orders of their superiors and the laws of their country. Most of their actions were recognized as being legal under the judicial system of the Third Reich. They were ultimately found guilty, nevertheless, of violating a higher law to which all nations and peoples are subject.

Sir Hartley Shawcross, the British prosecutor, stressed that there could be no immunity "for those who obey orders which -- whether legal or not in the country where they are issued -- are manifestly contrary to the very law of nature from which international law has grown." The prosecutors at Nuremberg built their case on the fact that, in the final analysis, the laws of man and of nations are subject to the laws of God and the Natural Law.

To discern the Natural Law and thereby perceive our moral obligations requires reflection, reason and discipline. The darkening of our reason and the weakening of our will that has subtly infected us because of sin can make it challenging, even two millennia following Cicero, to properly grasp our natural moral obligations. The Natural Law, nevertheless, represents an essential core of universal morality, serving as a key foundation for ethics, and an antidote to the lawlessness that tempts us in every age.

Father Tadeusz Pacholczyk, Ph.D. earned his doctorate in neuroscience from Yale and did post-doctoral work at Harvard. He is a priest of the Diocese of Fall River and serves as the Director of Education at The National Catholic Bioethics Center in Philadelphia. See www.ncbcenter.org.