Natural Law: Definition, History, and Examples

 In Articles, Ethics, Featured, Morality, Natural Law, Natural Theology, Nature, Philosophy, Thomas Aquinas

How do we know what’s good and what’s evil? How do we determine right from wrong? How do we decide what laws to pass? How do we know what human behaviors ought to be normative? These seem like tough questions. However, a close examination of nature and creation potentially give us the answers we need.

What is Natural Law? Natural Law is the theory within philosophy that asserts that the design and functions of the natural world help us to understand what is right and good. Natural Law theory asserts that God’s moral inclinations are intrinsically woven into the design of nature and creation, therefore, we can ascertain God’s intentions for humanity by closely examining the universe, its ordering, and its inhabitants.

The most influential person to teach about Natural Law was 13th century theologian Thomas Aquinas. The study of Natural Law comes out of the discipline of Natural Theology.


The Four (Five) Types of Law

Aquinas identified and explained four types of law:

  1. Eternal Law
  2. Natural Law
  3. Divine Law
  4. Human (Positive) Law

This taxonomy from Aquinas has been studied extensively in philosophy classes and law schools across the globe. Other Christian philosophers and theologians have identified a fifth type of law known as the jus gentium.

Let’s define these types of law:

Eternal Law is the set of good ideas, intentions, and inclinations that come from the mind of God that governed the creation of the universe and everything in it.

Natural Law are those good ideas, intentions, and inclinations that come from the mind of God that also happen to directly affect human beings and can be discovered through a close examination of the universe and human behaviors.

It can be said that Eternal Law was the wisdom of God that drove and informed the creation of the natural world, while Natural Law is the wisdom of God that can be seen and observed in the natural world.

Divine Law are the standards and expectations set by God for believers. It could be said that these are the standards that a person must follow to be considered holy in the sight of God. These are revealed only through special revelation.

Human Law (also called Positive Law) is what we most commonly think of when the word law is used. These are the standards and expectations set by a sovereign nation, local jurisdiction, human institution, or government entity.

The fifth type of law that other philosophers have identified is the jus gentium, which are those laws, regulations, and expectations which govern the relationships and interactions between sovereign nations. Some theologians, however, have argued that this type of law is not in a separate fifth category, but is a subset of Human Law, and should be examined accordingly.


Understanding Natural Law

Natural Law is rooted in Natural Theology, which is a genre of Christian theology that asserts that humans can learn a lot about God’s attributes and intentions by examining the universe, its functions, and its inhabitants.

The Bible commands us to learn from the natural world. There are dozens of commands in the Bible that point us toward nature and creation. My favorite example of this comes from Proverbs:

Go to the ant, O sluggard; consider her ways, and be wise. Without having any chief, officer, or ruler, she prepares her bread in summer and gathers her food in harvest” (Prov. 6:6-8 ESV).

Herein we see the Biblical author rebuking the lazy person, telling him to learn from the ants. As we examine this tiny creature we see things that we ought to embrace, mainly hard work and the willingness to prepare for the coming season.

God intends for us to work hard, to be wise, and to be prepared. The precedent being set for us here with his Proverb is that there are things in nature that teach us God’s intentions for us. We can learn from the cosmos, creation, and the animal kingdom—even ants.


God’s Moral Inclinations on Display

Proponents of Natural Law often contend that humans can recognize God’s moral inclinations that are on display in nature and creation because all human beings already possess some knowledge of God and his moral inclinations; such knowledge is stamped into the soul of every person, even if many humans deny having any such knowledge.

Aquinas argued that at creation God imprinted human beings with his own moral inclinations. He said:

God has imprinted in creatures their inclinations to their proper acts and ends, in accordance with God’s eternal plans” (Summa Theologica, I-II, Q.93).

Therefore, humans have inclinations toward proper and good behaviors. If humans follow these good inclinations they will flourish and fulfill God’s plans for humanity. Of course, sin corrupts humanity which makes it difficult for humans to follow those good inclinations (and there are some Christian theologians that contend it’s not merely difficult, it’s actually impossible).

By examining nature and creation, humans are not learning brand new moral material; humans are actually able to identify what is good and right because they already have some innate knowledge of such things. When a person says something like, “I just know that behavior is wrong” they are often speaking from some innate sense of morality that was imprinted upon them by God, even if they deny the existence of God.


Imprinted on Our Hearts? Does the Bible Agree?

As previously mentioned, Aquinas contended that Eternal Law is imprinted on the hearts of humans, and we can gather or obtain a good understanding of Natural Law by examining the natural inclinations of human beings. But what does the Bible say? Would the Biblical authors endorse Aquinas’ idea?

The apostle Paul writes, “For what can be known about God is plain… his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived.” He later says this is why “they are without excuse” (Rom. 1:18-20 ESV).

One chapter later Paul says, “For when Gentiles, who do not have the law, by nature do what the law requires… They show that the law is written on their hearts, while their conscience also bears witness” (Rom. 2:14-16 ESV).

In these passages we see the apostle Paul making clear that various truths about God can be seen by examining nature. We also see that there is some knowledge of God, and of his moral inclinations, inherently known to human beings. It could be said, in someway, God’s morality is intrinsically woven into the human psyche.

Of course, that does not mean that humans have a complete or full knowledge of God’s attributes or intentions. The writer of Ecclesiastes makes a similar statement when he says, “Yet God has made everything beautiful for its own time. He has planted eternity in the human heart, but even so, people cannot see the whole scope of God’s work from beginning to end” (Ecc. 3:11 NLT).

As we examine these verses we observe that human beings certainly know enough about the moral inclinations of God that we should behave differently than we do. We humans are born knowing enough about God that we should live more righteously than what we typically do therefore, since we have some knowledge of God’s moral inclinations, God would be right and just to condemn us. As the apostle Paul says, we are “without excuse.”

God’s intentions for humanity (and the human behaviors that are in accordance with God’s intentions) are “imprinted” on the hearts of human beings. The tragedy of humanity is not that humans are ignorant, but that human beings continually choose to behave wrongly or sinfully despite our knowledge of God.


Biblical Ethics Corroborated, Even by Pagans

Interesting observation, several ancient cultures had various laws and structures in place that rewarded good behavior that the Bible would endorse. Those same societies also had punishments in place for behaviors the Bible would condemn or prohibit. It seems that the ability to rightly determine what is right and wrong is indeed intrinsic (to some extent).

In addition, several well-known pagan and secular philosophers have come to conclusions very similar to what the Bible teaches. But, of course, these people did not attain their understandings of ethics from the Bible but by examining nature and creation; they championed morality that happened to be in-line with the teachings of Scripture, despite primarily relying on their observations of the natural world in lieu of the Bible. This includes world-renowned thinkers such as Socrates, Aristotle, Plato, Seneca, Cicero, Gratian, John Locke, Thomas Hobbes, David Hume, and Adam Smith.


Natural Law as the Basis for Human Law

Aquinas contended that Human Laws are only valid if they conform to what we learn from Natural Law.

Aquinas said, “Every human law has just so much of the nature of law as is derived from the law of nature. But if in any point it deflects from the law of nature, it is no longer a law but a perversion” (Summa Theologica, I-II, Q.95).

Following Aquinas’ thinking, any Human Law that violates Natural Law is invalid.

Proponents of Natural Law have often argued that we ought to look to the natural order of all things to determine which human behaviors ought to be normative, celebrated, and promoted. Natural Law theory proponents would encourage us to examine the biology, physiology, history, and tendencies of humanity to learn which structures seem ideal.

This, of course, is dependent on the notion that there are certain structures, behaviors, and actions that are inherently good for humans, causing them to flourish, while there are other structures, behaviors, and actions that inherently impede humanity’s ability to flourish, and that this is universal to all people, anywhere and at all times.

Whatever is good for Americans is also good for Africans and Europeans. Whatever causes men to flourish also causes women to flourish. Whatever was morally right and best for humans in the first century is still morally right and best for humans living today. With these principles for human flourishing in mind, proponents of Natural Law theory contend that Human Laws ought to be rooted in whatever universally causes humans to flourish.

If there happens to be any group of human beings that are not flourishing within any particular society, it is likely because some principle of Natural Law is being violated.


Examples of Natural Law

Natural Law theory is best understood by examining specific contemporary examples.

Why Do We Outlaw Murder?

This example will seem obvious, but it’s a good place to start. The reason we outlaw murder is because it impedes human flourishing. If humans are killing other humans, then those humans are obviously not flourishing, right? A society where people are murdering other people would also lead to many people living in fear; they would structure their lives around surviving a potential attack, rather than contributing to the society.

You can quickly see how allowing murder would allow lead the humans of that society to lack the ability to flourish. Therefore, according to Natural Law, since we can observe that murder within a society would impede human flourishing, we can rightly deduce that murder is immoral. It can be said that the immorality of murder is baked into human design, therefore murder being wrong is a Natural Law.


Martin Luther King Leveraged Natural Law

In 1963, Martin Luther King wrote his famous, “Letter from a Birmingham Jail.” Therein he appealed to both the Bible and to Natural Law. He first contended that the Bible condemns racial injustice and oppression, calling upon Christians to fight for civil rights.

He also appealed to Natural Law, asserting that racial injustice impedes human flourishing, both for Black people and White people. He argued that we know that some laws and policies are unjust because we can observe how they negatively impact Americans. The fact that many Americans were not flourishing in various regions of the country was evidence that some Natural Laws were being violated.

The Cry for Justice is Natural

Aquinas identified several key inclinations within human beings. One of them being the inclination to live in a society that promotes justice. Aquinas acknowledged that many people live contrary to their own inclinations because of sin, but that if we look closely we ultimately see the desire for justice at the core of the human heart. Everyone, everywhere wants justice.

People get angry when injustice is allowed. And humans are content when they sense justice being served. This demonstrates that justice must be a good thing. The desire for justice is fundamental to so many humans that this shows us that justice is a good thing. Societies ought to be structured with justice in mind.

Why Parents Love Their Children?

It is natural for parents to love their children. This is inherent in humans, in every culture throughout history. Also, we see that when immature persons (typically younger adults) become parents, they often rise to the challenge; there’s an accelerated maturing process that seemingly takes place. This benefits society. In addition, when parents care for their children well, we obviously see that the children flourish. All of this teaches us that it is morally right for parents to care for their children; society ought to celebrate parents who care for their children and implement structures that support those parents.

Proponents of Natural Law would explain this as being a part of the divine design of humanity; parents love their children because they are designed by God to care for their children. Any Human Law created relating to children would not need to necessarily make humans feel like they ought to care for their children since such feelings are universally inherent. However, if there are parents that fail to care for their children, society ought to condemn that failure as being unnatural—and since it is unnatural it is immoral. The government ought to compel (and hold accountable) any parent that does not care for their child.


Natural Law Arguments Against Same-Sex Sexual Behavior

This is the last example I will use in this article, and it’ll certainly be more controversial than the other examples herein, but is worth considering.

When discussing same-sex relations, Christians have traditionally condemned homosexual acts on the basis of Scripture. That is a perfectly valid approach. However, another approach could be to utilize and leverage Natural Law.

Argument #1: The simplest argument would be to examine human anatomy. The anatomy of men seems to go with the anatomy of women. They literally fit together. Therefore, it’s reasonable to deduce that men should be having sex with women, not men.

Argument #2: Consider reproduction. A man and a woman can make a baby. Two men cannot procreate, therefore the natural design of humanity seems to be telling us that men should be seeking women, not other men.

Argument #3: As we examine history, we observe that one necessary item for societies to flourish is long-term is population growth. Now, some societies grow in population numbers and yet still decline, for other reasons, but what we do not see in history is any society declining numerically over a long period of time and yet continuing to flourish and function well. Therefore, it can be said that societies are to seek to numerically grow. Procreation is important. Therefore, societies are to be ordered with procreation in mind. Since two men cannot procreate, that should be outside of the bounds of what is considered normative.

Argument #4: Some proponents of Natural Law theory have argued that the psychological impact of same-sex relations is different than the psychological impact of natural sexual relationships. Interestingly enough, the first person on record to make these claims was not a Bible-believing Christian, but the ancient Greek philosopher Plato. In The Symposium, Plato expresses his concern with the appetite portion of the human soul, which he contended needed to be controlled if human were to be the best versions of themselves. Because he saw same-sex passions as being especially strong and erotic, he argued that indulging in such passions would harmful.

Argument #5: In our modern era, a person could cite the tremendous data that points to the fact that children, in order to flourish, need a mom and a dad. Since this cannot ever be accomplished if we allow men to marry men or women to marry women, we could argue that the only valid marriages would be between a man and a woman; or at least we could argue that same-sex couples ought not be permitted to adopt children.


Aristotle and the History of Natural Law

Aristotle is often associated with Natural Law. In fact, he has sometimes been called the Father of Natural Law. However, this is actually mostly because Aquinas frequently utilized and leveraged Aristotle’s writings to explain Natural Law.

Aquinas was greatly influenced by philosopher Albertus Magnus. Magnus extensively studied Aristotle, which inspired Aquinas to do the same. Largely building on Aristotle’s writings, Aquinas developed ideas focused on how Natural Theology ought to be utilized in the fields of politics and ethics, which led to his writings on Natural Law.

Aquinas argued that human beings, using reason and intellect, could carefully examine how humans function and behave in the natural world, and that such examinations could lead humans to appropriately determine how God intends for humans to live. Aquinas posited that humans could figure out what behaviors and structures would help society flourish. Once we determine what leads to societal flourishing, we’ll have a good understanding of what is right and wrong, and we have the basis for societal structures and policies.

[Side Note: There have been several modern scholars that claim Aquinas misunderstood Aristotle, that Aristotle did not necessarily argue for the concepts of Natural Law, as articulated by Aquinas. But even if Aquinas misunderstood Aristotle, Aquinas’ interpretation of Aristotle has been very influential for several centuries, and it’s unlikely that will be undone anytime soon.]


Natural Law Misused During the Enlightenment

It is clear that Aquinas never intended for anyone to use his ideas as reason to abandon Christianity—quite the opposite is true. Aquinas’ vision was that people would use their reason to deduce what is morally right or wrong, and eventually they would see that the Bible just so happens to be on the right side of every moral debate.

Aquinas believed that people would come to conclusions on various ethical or moral debates, and that they would notice that Christianity is the religion which leads to true human flourishing which, in theory, would cause many people to realize that Christianity must be the true religion. He was convinced that a proper use of reason would corroborate the Bible.

However, during the (so-called) Enlightenment Era, a strange movement arose. Several philosophers used the ideas of Natural Theology and Natural Law to do the exact opposite of what Aquinas had intended. Various philosophers argued that we no longer needed the Bible as the basis for our ethics; there was no need for the Bible in modern society because we had Natural Law.

Several philosophers across Europe argued that we, human beings, can determine what is right and wrong simply by examining the natural world and by thinking deeply about the functions of humanity. With this in mind, they saw no need for the Bible or for traditional orthodox Christianity.

Aquinas articulated his ideas of Natural Law as a means of pointing people towards the value of having the Bible as authoritative in their lives, but many of these Enlightenment thinkers manipulated Aquinas’ ideas, going in the exact opposite direction than what Aquinas would have intended. This way of thinking largely influenced several of the founders of the United States. The language of Natural Law is prevalent in American founding documents and literature, most notably in the Declaration of Independence.



While the Bible is certainly the primary source of truth, especially knowledge of God’s attributes and intentions, we can still learn from nature and creation. Arguments from Natural Law can be helpful in our apologetic conversations and in our political discourse. We ought to seek to protect all peoples and seek the common good, and arguments from Natural Law will likely be helpful to us as we seek to do that.

Many of these types of conversations will be with persons who have rejected the Bible, however, by effectively using Natural Law, we may be able to convincing argument for Biblical ethics. Such efforts is a Christ-exalting endeavor!